The authors examined 1293 sportsmen engaged in different types of sporting activity and of a different level of mastership in their line and 482 young men who never went in for sports. They were subjected to electrocardiographic investigations with continuous recording of 100 cardiac cycles. The ECG analysis showed that sportsmen have disorders of cardiac rhythm in a statistically significant higher proportion of cases. The depressed activity of the sinus pacemaker is especially frequent which shows "arrhythmias of depressed sinus node" and extrasystoles. The latter in sportsmen are due to pathological changes related to the foci of chronic infections, myocardial dystrophy due to chronic physical overexertion and marked myocardial hypertrophy.