Climbing above 4,000m can provoke abnormal heart rhythms in otherwise healthy mountaineers, with the abnormalities increasing with altitude, new research has shown. The study, by sports scientists at Leeds Beckett University and cardiologists at Poole Hospital, found that in a team of 16 healthy mountaineers, without a previous history of heart disease, more than half experienced rhythm disturbances at altitudes of 4,100 metres or above.