More than a million people in the UK now live with a condition that causes the heart to beat irregularly and can lead to strokes.
Data from the British Heart Foundation (BHF) shows the UK has, for the first time, topped the million mark in the number of people diagnosed with a trial fibrillation.
The figure is up almost 20% on five years ago. High blood pressure, heart valve disease and binge drinking are among the causes alongside the fact people are living longer.
The heart condition causes an irregular and often abnormally fast heart rate, frequently leading to dizziness and shortness of breath.
Sufferers may also feel palpitations and become very tired.
A normal heart rate should be between 60 and 100 beats a minute when a person is resting, with a regular rhythm.
Some people with atrial fibrillation have no symptoms and are completely unaware that their heart rate is irregular.
If left untreated, atrial fibrillation can significantly increase the risk of a blood clot forming inside the heart, which increases the risk of stroke five-fold.
The BHF said atrial fibrillation is responsible for 22,500 strokes a year in the UK.
Simon Gillespie, chief executive of the charity, said: "The real danger with atrial fibrillation is that some people don't realise they have it. You can be going about your daily routine oblivious to the fact you're five times more likely to have a devastating stroke.
"Checking that your pulse is regular is a simple way of seeing if you're at risk. But only through research can we tackle this dangerous disorder and prevent its devastating consequences."
The data was released as part of the BHF's Ramp up the Red fundraising campaign.
Richard Elgar, 43, from Dorset, was diagnosed with atrial fibrillation last September.
The father-of-two, who is a builder, said: "I'd already had a heart attack when I was 36, so finding out I had atrial fibrillation was another blow.
"I didn't tell my wife about the risk of stroke until I was on medication to help prevent it. I didn't want to worry her and the children. But every tiny ache or twinge still makes me panic that something could be starting that could devastate my family. It's incredibly stressful.
"I'm currently waiting for further treatment, so I'm not out of the woods yet. More research, funded by the BHF's Ramp up the Red campaign, could help find better ways of treating people like me and make sure my family stays together. We're all set to dig out our reddest outfits for the occasion and I hope thousands of other families will join in too."
Mr Elgar's eldest son Alfie, eight, completed a 40-mile bike ride last summer to raise funds for the BHF. He continued despite falling off his bike twice because of the heat and exhaustion.
The schoolboy has said he wants to be a heart surgeon when he grows up so he can "fix daddy".