Study shows why some stroke patients do not have abnormal heart rhythms Scientists have shed light on why some people who have a stroke do not also have abnormal heart rhythms, even though their hearts contain similar scar tissue. Their results, published today in eLife, could help identify the best treatments for people who might be at risk of recurrent stroke, new heart disorders, or both. Strokes are often caused by abnormal blood flow resulting from rapid, irregular beating in the upper chamber of the heart. This is also called atrial fibrillation (AFib). But some people have strokes that appear to have been caused by the heart, yet there is no evidence of AFib. In fact, around 25% of strokes fall into this group - called embolic strokes of undetermined source (ESUS).