People are being urged to check their pulse for a condition that causes around 16,000 strokes every year.
Atrial fibrillation affects around 800,000 people in the UK and is characterised by an abnormal heart rhythm.
Those over 55 are most at risk and could have up to five times the chance of suffering a stroke as healthy people.
Blood thinning treatments are available if the condition is caught early.
The British Heart Foundation (BHF) launched a new campaign to raise awareness of atrial fibrillation.
A survey of more than 2,000 members of the public found people were far more likely to check their passport expiry date (57%) than their pulse (32%).
Only 28% of people knew taking their pulse was a health check they should carry out on themselves.
This compared with 89% who knew about self-checks for breast cancer and 90% who knew to check for testicular cancer.
The BHF has launched a dedicated phone line (0300 333 2 333) and new area of its website (bhf.org.uk/pulse) so people can hear examples of regular and irregular heartbeats, and get advice on how to take their pulse.
Broadcast doctor and journalist Rosemary Leonard said: "Checking your pulse is so simple - you really don't need to be a doctor or a nurse. The BHF phone line and website will help you take your pulse and help you understand what an irregular rhythm could feel like. Taking one minute, check yours - don't leave it to chance."
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