Heart failure and hot weather:
how to manage fluids and diuretics in summer

Article written and reviewed by Dr Luca Moretti

Very hot weather requires particular attention in heart failure because vasodilation and sweating can reduce blood pressure and circulating volume, while diuretics and other medications can amplify the risk of dehydration, hypotension, and electrolyte abnormalities. At the same time, drinking excessive amounts or reducing diuretics on your own can promote congestion.
The correct strategy is therefore neither to "drink as much as possible" nor to rigidly maintain the same restrictions under all conditions, but to adjust fluids and treatment according to the individual plan.

On very hot days, it is useful to:

• avoid physical activity during the hottest hours and favor cool environments;
• monitor blood pressure, weight, and symptoms more closely if this is normally recommended;
• adjust fluid intake according to the instructions received and losses due to sweating;
• not change diuretics or other medications on your own unless there is an agreed written plan;
• quickly recognize dizziness, weakness, hypotension, or signs of congestion;
• seek medical assistance if important symptoms or symptoms that are difficult to interpret occur.

Older people, those with kidney disease, already low blood pressure, or advanced heart failure are particularly vulnerable to the effects of high temperatures.

Why hot weather can put the heart and circulation under stress

To dissipate heat, the body increases blood flow to the skin through vasodilation. Peripheral resistance decreases and the heart must compensate by increasing cardiac output, often also through an increase in heart rate. Sweating also causes loss of water and electrolytes.
In a person with reduced cardiac capacity, these adaptations may be less efficient and increase the risk of fatigue, hypotension, ischemia, or arrhythmias.

The 2025 ESC scientific statements and the 2026 AHA scientific statement emphasize that extreme temperatures increase cardiovascular morbidity and mortality and that people with cardiovascular disease are among the most vulnerable groups. In heart failure, diuretics can accentuate volume and electrolyte loss during hot weather.
This does not mean that medications should be stopped: it means that on days of extreme heat some patients require closer monitoring and a more careful plan.

How much to drink when the weather is very hot

Contemporary recommendations do not support rigid fluid restriction for all patients with stable heart failure. The HFA/ESC consensus on sodium and fluids generally considers an intake of about 1.5-2.5 liters per day to be normal, adjusted according to thirst and environmental conditions; restrictions of 1.5-2 liters are used mainly in selected patients with severe heart failure or hyponatremia.
During very hot weather and high humidity, losses increase and it may be necessary to drink more fluids than on a cool day.

However, it is not possible to specify an additional amount that is valid for everyone. A person with persistent congestion and hyponatremia has different needs from a stable patient who has low blood pressure and intense sweating. Anyone following a fluid restriction should therefore ask the care team how to adjust it during heat waves.
The 2025 FRESH-UP trial also showed that, in outpatients with stable chronic heart failure, a liberal fluid strategy compared with restriction to 1.5 liters per day did not increase safety events and reduced thirst-related distress.

Diuretics and other medications: what not to do on your own

Loop diuretics increase the elimination of sodium and water and are essential when congestion is present. In very hot weather, however, a person who sweats heavily and continues to take the same dose can become hypovolemic more easily, with dizziness, hypotension, worsening kidney function, or sodium and potassium abnormalities.
Conversely, reducing the diuretic on your own while still congested can promote fluid accumulation and an exacerbation of heart failure.

The dose should therefore be changed only according to an individualized plan based on weight, blood pressure, edema, breathing, urine output, and any relevant tests. ACE inhibitors, ARNIs, ARBs, mineralocorticoid receptor antagonists, SGLT2 inhibitors, and other medications can also contribute to lowering blood pressure or circulating volume in certain circumstances, but they should not be stopped preventively every summer.
If repeatedly very low blood pressure readings occur together with dizziness, syncope, marked fatigue, or rapid weight loss, the physician should be contacted to reassess treatment and hydration.

How to reduce heat exposure in everyday life

The most effective measure is to reduce heat load. During the hottest hours, it is preferable to stay in a cool environment, use ventilation or air conditioning when available, wear light and breathable clothing, and limit strenuous outdoor physical activity. Walking and exercise can be moved to early morning or evening.
During a heat wave, it may be necessary to temporarily reduce the duration and intensity of physical activity, especially if the same exercise causes more shortness of breath or fatigue than usual.

Alcohol promotes dehydration and can interfere with blood pressure and medications; large amounts are therefore particularly unsuitable on very hot days. Large meals and very crowded, poorly ventilated environments can also increase discomfort.
People who live alone, are older, or have limited independence should have a simple plan for maintaining a sufficiently cool environment and for contacting someone if their condition worsens.

Dehydration or congestion: which signs to watch for

The practical difficulty is that a person with heart failure must avoid both excessive fluid loss and fluid accumulation. Intense thirst, dry mouth, dizziness when standing up, blood pressure lower than usual, weakness, reduced urine output, and rapid weight loss point toward dehydration or reduced circulating volume.
Conversely, weight gain, increasing edema, greater shortness of breath, the need for more pillows, and waking at night gasping for air suggest congestion above all.

This distinction is not always straightforward. A person can have peripheral edema and, at the same time, reduced effective arterial blood volume, especially in advanced forms. For this reason, important symptoms, persistent low blood pressure, or rapid weight changes require assessment rather than repeated self-adjustments of water intake and medications.
Signs of deterioration are discussed in greater detail in the guide on worsening heart failure.

Confusion, altered consciousness, fainting, inability to remain standing, very high body temperature, or rapid deterioration in general condition may indicate severe heat illness. Chest pain, severe breathing difficulty, or palpitations associated with syncope also require urgent medical attention.
In these situations, it is appropriate to call 112 or 118 and move the person to a cooler environment while following the emergency dispatcher's instructions.

A less dramatic but progressive deterioration, such as recurrent dizziness, blood pressure persistently lower than usual, reduced urine output, rapid weight loss, or increasing shortness of breath, still warrants prompt contact with the care team. The goal is to correct the problem early without waiting for it to progress to severe dehydration or acute decompensation of chronic heart failure.

Frequently asked questions about heart failure and hot weather

With heart failure, should you drink more when the weather is hot?
Fluid intake may need to be adjusted, especially during very hot weather, high humidity, or increased sweating. However, there is no single amount that is right for everyone: people on fluid restriction should agree with their care team on how to modify it on hot days.

Should diuretics be reduced in hot weather?
Not automatically and not without an agreed plan. Hot weather can increase the risk of dehydration, hypotension, and electrolyte abnormalities, but reducing the diuretic too much can promote congestion. Weight, blood pressure, symptoms, and kidney function guide the decision.

Which signs may indicate dehydration?
Intense thirst, dry mouth, dizziness, weakness, blood pressure lower than usual, reduced urine output, and rapid weight loss may suggest excessive fluid loss, especially if they occur during a period of hot weather.

How can you tell whether the problem is dehydration or worsening heart failure?
It is not always possible to distinguish them on your own. Weight gain, edema, and orthopnea point more toward congestion; rapid weight loss, thirst, dizziness, and hypotension point more toward volume loss. Complex situations can coexist, however, and clinical assessment is needed.

When does hot weather require urgent medical attention?
Confusion, fainting, severe weakness, very high body temperature, severe breathing difficulty, chest pain, or altered consciousness require urgent medical attention and may make it necessary to call 112 or 118.