Researchers identify heart block cause in athletes While heart block is benign for most people, it can be a precursor to more serious heart problems. 23 June, 2021 23:01 Why some endurance athletes experience a heart rhythm disturbance called heart block has been identified by researchers using animal models. The University of Manchester-led study found that long-term exercise in retired racehorses – the best available model of the athlete’s heart – and in mice, triggered molecular changes in a part of the heart known as the atrioventricular (or AV) node. Despite well-recognised cardiovascular benefits, sustained endurance exercise in athletes, footballers and other sportspeople can lead to the development of abnormal heart rhythms – known as cardiac arrhythmias, including heart block.