Why does dehydration cause palpitations?

Water and salts help maintain blood volume and support normal electrical activity in the heart. When fluid is lost through heat, sweating, vomiting, diarrhoea, fever, or not drinking enough, there is less fluid moving through the circulation. The body may respond by increasing the heart rate, which can feel like racing, thumping, skipping, or fluttering. Palpitations are a common presentation of dehydration, but they can also have other causes.

A dry mouth, thirst, dark urine, dizziness on standing, headache, tiredness, or reduced urination can occur alongside fluid loss. Heavy sweating or stomach illness may also disturb electrolyte balance, which can add to the sensation of an unsettled heartbeat.

Move to a cooler place and rest if heat or exertion may have contributed. Take small, frequent sips of water; an oral rehydration drink can be useful when vomiting, diarrhoea, or heavy sweating has caused losses. Avoid alcohol and large amounts of caffeine while the sensation is present, as both can worsen dehydration or make the heartbeat more noticeable.

Notice whether the palpitations settle as you rehydrate and rest. If you take medicines that affect fluid balance, or have heart, kidney, or liver disease, get personalised advice before deliberately increasing fluids.

Seek urgent medical help for palpitations with chest pain, severe shortness of breath, fainting, confusion, new weakness, or a heartbeat that remains very fast or irregular at rest. Get same-day clinical advice if you cannot keep fluids down, pass very little urine, have persistent dizziness, or the palpitations keep returning. These warning signs need assessment regardless of the suspected trigger.

Ask whether your symptoms fit dehydration, whether an ECG or blood test is appropriate, and how much fluid is sensible for your health conditions and medicines. Mention recent illness, heat exposure, exercise, supplements, caffeine, and any history of abnormal heart rhythm.