Hot weather can put extra strain on the heart. For many people, a warm summer day is uncomfortable but manageable. For someone with a heart condition, high blood pressure, heart failure, angina, atrial fibrillation or a history of heart attack or stroke, heat can make symptoms worse and increase the risk of dehydration, dizziness, low blood pressure, palpitations and heat illness.
This does not mean everyone with a heart condition must avoid summer completely. Most people can stay well with sensible precautions: drinking enough fluids, avoiding the hottest part of the day, keeping the home cool, taking medicines safely, recognising warning signs early and asking for medical advice if symptoms change.
However, hot weather should be taken seriously. Heatwaves can be especially risky for older adults, people with long-term heart or lung conditions, people taking water tablets or blood pressure medicines, and anyone who lives alone or finds it difficult to keep cool at home.
This guide explains how hot weather affects the heart, which heart conditions need extra care, how medicines can be affected, what symptoms to watch for, and when to call NHS 111 or 999.
Quick answer: Hot weather can make the heart work harder because the body sends more blood to the skin to release heat. Sweating can also lead to dehydration, which may lower blood pressure and trigger dizziness, palpitations or kidney strain. People with heart disease, heart failure, angina, atrial fibrillation, high blood pressure or those taking diuretics should take extra care during heatwaves and seek help if symptoms worsen.
Why hot weather affects the heart
When the weather is hot, the body has to work harder to keep its temperature under control. Blood vessels near the skin widen so heat can escape, and sweating helps cool the body as moisture evaporates.
This cooling system is useful, but it places extra demands on the circulation. The heart may need to pump more blood towards the skin, while sweating can reduce fluid and salt levels. For someone with a healthy heart, this may simply feel uncomfortable. For someone with a heart condition, it can sometimes tip the balance.
Hot weather can contribute to:
- faster heart rate
- lower blood pressure
- dizziness or faintness
- dehydration
- palpitations
- angina symptoms in some people
- worsening breathlessness
- fluid balance problems in heart failure
- greater strain on the kidneys
- heat exhaustion or heatstroke
The British Heart Foundation advises heart patients to drink plenty of fluids in hot weather, avoid the hottest part of the day and take extra care if they have been told to restrict fluid intake because of heart failure. British Heart Foundation hot weather advice.
For wider background, see Cardiovascular Risk: Heart Attack and Stroke Prevention, High Blood Pressure and Heart Palpitations.
Who is most at risk in hot weather?
Anyone can become unwell in a heatwave, but some people with heart or circulation problems need extra care.
Higher-risk groups include people with:
- heart failure
- angina
- coronary heart disease
- previous heart attack
- atrial fibrillation or other rhythm problems
- high blood pressure
- low blood pressure or frequent dizziness
- heart valve disease
- previous stroke or TIA
- diabetes
- kidney disease
- long-term lung disease as well as heart disease
Risk is also higher for older adults, people who live alone, people with dementia, people with reduced mobility and those taking medicines that affect fluid balance, blood pressure, urination or sweating.
GOV.UK states that anyone can become unwell if they get too hot, but some people are at higher risk of becoming seriously unwell and may need extra support during hot weather. GOV.UK Beat the Heat guidance.
Useful related guides include Heatwave Safety for Older Adults, Stroke Symptoms and TIA, Diabetes Explained and eGFR and Creatinine Results.
Dehydration, blood pressure and dizziness
Dehydration is one of the main reasons hot weather can affect people with heart conditions. When you sweat more than usual and do not replace enough fluid, blood volume can fall. This may lower blood pressure and make the heart work harder.
Possible signs of dehydration include:
- thirst
- dry mouth
- dark yellow urine
- passing urine less often
- dizziness
- headache
- tiredness
- confusion, especially in older adults
- muscle cramps
For people with blood pressure problems, dehydration can cause light-headedness, fainting, falls or worsening kidney function. It can also make palpitations feel more noticeable.
In hot weather, many people need to drink more than usual. Water is usually best, but milk, diluted squash and other non-alcoholic drinks can also contribute. If you have been told to restrict fluids because of heart failure or kidney disease, do not simply drink large amounts without advice. Speak to your GP, heart failure nurse or specialist team about how to stay cool safely.
For more detail, see Dehydration Symptoms in Adults and Children, Dizziness: Common Causes and When to Worry, Fainting and Blackouts and Home Blood Pressure Monitoring.
Heart medicines and hot weather
Some medicines can make hot weather more difficult to manage. This does not mean you should stop taking them. It means you should be aware of possible effects and ask for advice if you feel unwell.
Medicines that may need extra awareness during heatwaves include:
- diuretics, also called water tablets, which increase urination and may raise dehydration risk
- ACE inhibitors and ARBs, which can affect blood pressure and kidney function during dehydration
- beta-blockers, which can affect heart rate response and heat tolerance in some people
- calcium channel blockers, which can lower blood pressure and sometimes worsen ankle swelling
- nitrates, such as GTN spray, which can lower blood pressure and cause dizziness
- blood thinners, which do not directly cause overheating but may matter if falls occur
- diabetes medicines, because dehydration and heat can affect blood sugar and kidney strain
The MHRA advises that some medicines can make it harder for the body to regulate temperature or can increase dehydration risk. It specifically highlights diuretics and blood pressure medicines such as ACE inhibitors, beta-blockers and calcium channel blockers during hot weather. MHRA hot weather medicines advice.
Do not stop heart medicines without medical advice. Stopping suddenly can be dangerous, especially with medicines for blood pressure, angina, heart rhythm problems or heart failure. Instead, speak to a pharmacist, GP or specialist team if you feel dizzy, faint, unusually weak, dehydrated, confused, short of breath or unable to keep fluids down.
For related topics, see Statins Explained, Cholesterol Blood Test Results and What to Do After Abnormal Private Blood Test Results.
Heart failure and hot weather
Hot weather can be particularly tricky for people with heart failure because there is a balance between avoiding dehydration and avoiding too much fluid. Some people with heart failure are advised to limit fluid intake, while others may need to drink more during heatwaves. This should be individualised.
Speak to your heart failure nurse, GP or specialist team before a heatwave if you:
- have been told to restrict fluids
- take water tablets such as furosemide, bumetanide or spironolactone
- have frequent dizziness or low blood pressure
- have kidney function problems
- have had recent heart failure flare-ups
- are unsure what to do if your weight changes quickly
Warning signs that heart failure may be worsening include:
- increasing breathlessness
- waking at night short of breath
- needing more pillows to sleep
- rapid weight gain over a few days
- swollen ankles, legs or abdomen
- unusual tiredness
- reduced exercise tolerance
Heat exhaustion and heart failure can overlap. For example, tiredness, dizziness and weakness may be dehydration, but worsening breathlessness or swelling may suggest fluid retention. If symptoms change, seek medical advice rather than guessing.
See also Swollen Legs and Ankles, Shortness of Breath and U&E Blood Test Results Explained.
Angina, chest pain and exertion in the heat
Hot weather can make physical activity harder. The heart is already working to help cool the body, and dehydration can lower blood pressure. For some people with angina or coronary heart disease, this can make chest tightness or breathlessness more likely during exertion.
To reduce risk:
- avoid strenuous activity during the hottest part of the day
- plan essential outdoor tasks for early morning or evening
- stay in the shade where possible
- take regular breaks
- carry water
- keep prescribed angina medicines, such as GTN spray, with you
- avoid rushing, carrying heavy shopping or climbing many stairs in strong heat
If you use GTN spray, remember it can lower blood pressure and may make dizziness worse, especially in hot weather. Sit down before using it if possible and follow the plan given by your clinician.
Call 999 if chest pain is severe, new, does not improve with rest or prescribed angina treatment, or is associated with sweating, nausea, breathlessness, faintness or pain spreading to the arm, jaw, neck, back or stomach.
For more detail, see Chest Pain: When to Worry and When It’s Not Your Heart and ECG Results Explained.
Atrial fibrillation, palpitations and heat
Some people notice more palpitations in hot weather. This can happen because of dehydration, poor sleep, alcohol, caffeine, stress, illness, fever, or changes in blood pressure. Heat may also make existing rhythm symptoms more noticeable.
If you have atrial fibrillation, hot weather may affect how you feel day to day, especially if you become dehydrated or drink more alcohol than usual. Keeping fluids steady, avoiding excess alcohol and resting in cooler places can help reduce strain.
Seek medical advice if palpitations are:
- new or different from usual
- persistent
- associated with chest pain
- associated with fainting or near-fainting
- associated with severe breathlessness
- accompanied by a very fast or irregular pulse that does not settle
Call 999 if palpitations come with chest pain, collapse, severe breathlessness, stroke symptoms or severe weakness.
Related guides include Atrial Fibrillation and Stroke Risk, Heart Palpitations, Health-Monitoring Smartwatches and Stroke Symptoms and TIA.
High blood pressure in hot weather
Blood pressure can behave differently in hot weather. Some people find it drops because blood vessels widen and they lose fluid through sweat. Others may see readings rise because of stress, poor sleep, dehydration, pain, alcohol, missed medicines or heat-related strain.
If you monitor blood pressure at home, do not panic over one reading. Rest quietly, drink if you may be dehydrated, avoid caffeine or exercise beforehand, and repeat the reading correctly. Look at patterns rather than isolated numbers.
Seek advice if:
- you repeatedly have very low readings with dizziness or faintness
- you repeatedly have high readings despite taking medicine
- you feel unwell with blood pressure changes
- you have chest pain, severe headache, confusion, weakness or breathlessness
- you are unsure whether to adjust medicines
Do not change blood pressure medication without professional advice. During heatwaves, medicine decisions need to consider hydration, kidney function, symptoms and your usual cardiovascular risk.
Useful guides include Blood Pressure Chart Explained, High Blood Pressure and Home Blood Pressure Monitoring.
How to stay safe during hot weather if you have a heart condition
The aim is to reduce heat exposure, prevent dehydration and avoid sudden strain on the heart.
Practical steps include:
- stay out of direct sun during the hottest part of the day
- avoid strenuous activity between late morning and mid-afternoon
- drink regularly unless you have been told to restrict fluids
- limit alcohol
- wear loose, light clothing
- keep your home cool by closing curtains and windows when it is hotter outside
- open windows when the air outside is cooler and safe
- use fans or cooling methods sensibly
- take cool or lukewarm showers
- eat lighter meals if heavy meals make you uncomfortable
- keep medicines stored correctly and away from heat
- carry essential medicines when going out
- check in with someone if you live alone
The NHS advises keeping out of the heat where possible, staying in shade between 11am and 3pm, drinking extra fluids, avoiding excess alcohol, wearing light clothes and using cooling measures such as cool showers or cool water on the skin. NHS heatwave advice.
For sleep and older-adult safety, see How to Sleep in Hot Weather and Heatwave Safety for Older Adults.
Exercise, gardening and travel in the heat
Exercise is important for heart health, but heat changes what is safe and sensible. During a heatwave, usual activities may feel harder than normal. Gardening, carrying shopping, walking uphill or travelling on hot public transport can all count as physical strain.
Safer choices include:
- exercise early in the morning or later in the evening
- choose indoor activity in a cooler place
- reduce intensity and duration
- avoid heavy lifting or digging in strong heat
- take water with you
- stop if you feel chest discomfort, dizziness, palpitations or unusual breathlessness
- avoid crowded, overheated transport where possible
- plan routes with shade, seating and toilets
If you have been given cardiac rehabilitation or exercise guidance, follow that plan and adapt intensity during hot weather. Do not push through symptoms because “it is only the heat”.
Seek advice if heat repeatedly limits your activity or causes symptoms. It may mean your heart condition, medicines or hydration plan needs review.
When hot weather symptoms need medical help
Heat exhaustion can usually improve if the person cools down, rests and drinks fluids. Heatstroke is an emergency. Heart symptoms during hot weather also need careful attention because they may not be “just heat”.
Possible heat exhaustion symptoms include:
- tiredness or weakness
- dizziness
- headache
- heavy sweating
- feeling sick
- muscle cramps
- fast pulse
- thirst
- cool, clammy skin
If heat exhaustion is suspected, move to a cooler place, remove unnecessary clothing, cool the skin with water or a fan, and drink cool fluids if able. The NHS says heat exhaustion does not usually need emergency medical help if the person cools down within 30 minutes, but heatstroke is an emergency. NHS heat exhaustion and heatstroke guidance.
Call 999 if there is:
- chest pain
- severe breathlessness
- collapse or fainting
- confusion or not acting normally
- seizure
- signs of stroke, such as face drooping, arm weakness or speech problems
- very hot skin and not sweating despite heat
- symptoms that do not improve after cooling
- severe weakness or inability to drink
Call NHS 111 or contact your GP if you are struggling with heat symptoms, have worsening dizziness, dehydration concerns, new medication side effects, worsening heart failure symptoms, or you are unsure what to do.
Preparing before a heatwave
People with heart conditions should plan before the hottest days arrive, especially if they live alone, are older, have heart failure, take several medicines or have had previous heat-related illness.
A useful checklist:
- check the weather forecast and heat-health alerts
- ask your GP, pharmacist or specialist nurse about hot-weather medicine advice if needed
- know whether you have a fluid restriction
- keep drinks easy to access
- identify the coolest room in the home
- make sure fans are safe and working
- keep curtains or blinds ready to block sun
- check medicines are stored below the recommended temperature
- keep emergency contacts visible
- arrange check-ins with family, neighbours or carers
- know when to call NHS 111 or 999
The UKHSA Heat-Health Alert system provides warnings when temperatures are likely to affect health and wellbeing. UKHSA Heat-Health Alerts.
If someone also has dementia, frailty or difficulty managing at home, see What to Do if an Elderly Parent Is Not Safe at Home, Home Care: Types of Support and Night Care at Home.
Final thoughts
Hot weather can affect the heart by increasing the body’s cooling demands, lowering blood pressure, worsening dehydration and making symptoms such as dizziness, palpitations, breathlessness or chest discomfort more likely. People with heart failure, angina, atrial fibrillation, high blood pressure, kidney disease or diabetes need particular care.
Most heat-related problems can be reduced by planning ahead: stay cool, drink appropriately, avoid the hottest part of the day, review medicine concerns with a professional, store medicines safely, and act early when symptoms change.
Do not assume chest pain, severe breathlessness, collapse, confusion or stroke-like symptoms are “just the heat”. These symptoms need urgent help.
For official advice, see NHS heatwave advice, NHS heat exhaustion and heatstroke guidance, GOV.UK Beat the Heat, MHRA hot weather medicines advice and British Heart Foundation hot weather advice for heart patients.
This article is for general information only and should not replace medical advice. If you have a heart condition and develop chest pain, severe breathlessness, fainting, confusion, stroke symptoms or signs of heatstroke, call 999.
Frequently asked questions
Can hot weather make heart conditions worse?
Yes. Heat can make the heart work harder, lower blood pressure, increase sweating and raise dehydration risk. This may worsen dizziness, breathlessness, palpitations, angina or heart failure symptoms in some people.
Why do I get palpitations in hot weather?
Palpitations in hot weather may be linked to dehydration, poor sleep, alcohol, caffeine, stress, fever or changes in blood pressure. If palpitations are new, persistent, severe or linked with chest pain, fainting or breathlessness, seek medical advice.
Can heat affect blood pressure?
Yes. Heat can cause blood vessels to widen and may lower blood pressure, especially if you are dehydrated or taking blood pressure medicines. Some people may also see higher readings due to stress, poor sleep or dehydration.
Should people with heart disease drink more water in hot weather?
Many people need extra fluids during hot weather. However, if you have heart failure, kidney disease or have been told to restrict fluids, ask your GP, heart failure nurse or specialist team for personalised advice.
Can water tablets be risky in a heatwave?
Diuretics, or water tablets, can increase fluid loss through urination, which may raise dehydration risk during hot weather. Do not stop them without advice, but speak to a clinician if you feel dizzy, dehydrated or unwell.
Can beta-blockers affect heat tolerance?
Beta-blockers can affect heart rate response and may make heat or exertion feel different for some people. If you feel unusually weak, dizzy or breathless in hot weather, seek advice.
Can ACE inhibitors affect thirst?
The MHRA notes that ACE inhibitors can suppress the natural thirst response in hot weather, which may increase dehydration risk in some people. Drink regularly unless you have been told to restrict fluids.
Is it safe to exercise in hot weather with a heart condition?
It depends on your condition and symptoms. In general, avoid strenuous activity during the hottest part of the day, reduce intensity, drink appropriately and stop if you develop chest discomfort, dizziness, palpitations or unusual breathlessness.
Can hot weather trigger angina?
Heat can increase strain on the heart and may make angina more likely during exertion in some people. Use prescribed angina treatment as instructed and call 999 if chest pain does not settle or feels severe or unusual.
Can hot weather worsen heart failure?
Yes. Heat can disturb fluid balance, blood pressure and kidney function. People with heart failure should ask their heart failure nurse or GP for personalised advice, especially if they take diuretics or have fluid restrictions.
What symptoms should heart patients not ignore in hot weather?
Do not ignore chest pain, severe breathlessness, fainting, confusion, stroke symptoms, worsening swelling, rapid weight gain, persistent palpitations, severe dizziness or signs of heatstroke.
When should I call 999?
Call 999 for chest pain, severe breathlessness, collapse, confusion, seizure, stroke symptoms, suspected heatstroke, or symptoms that feel like a medical emergency.
Can hot weather affect heart medicines?
Yes. Heat can affect medicine storage, and some medicines can affect hydration, blood pressure or heat tolerance. Store medicines as instructed and ask a pharmacist or GP if you are unsure.
How should heart medicines be stored in hot weather?
Keep medicines away from direct sunlight, cars, windowsills and very hot rooms. Follow the storage instructions on the packet or patient leaflet. Ask a pharmacist if a medicine has been exposed to high heat.
What is the best room temperature for heart patients?
There is no single perfect temperature for everyone, but avoiding overheated rooms is important. Keep living spaces as cool as reasonably possible, especially bedrooms and rooms used during the hottest part of the day.
