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 atrial 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.
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Activists, including a young woman wearing a head scarf, spoke out in turn in front of the cameras assembled to hear leader Paul Nuttall.
Mr Farron's bizarre comment was made to an activist who came to watch the party leader speak in Cambridge on Thursday.
The US actor starred in Disney's 2004 film Miracle, chronicling the US men's hockey team at the 1980 Winter Olympics.