The results of echocardiographic studies on 90 athletes representing various sport-types and 18 non-athletic persons are presented. The intracardiac diameter measured by echocardiography was proportional to the heart volume determined radiologically. The thickness of the septum and posterior heart wall compared to the internal heart diameter was greater in athletes with static exercise than in endurance athletes. This must be interpreted as a tendency to concentric hypertrophy. In endurance athletes this relationship tended to be less than in non-athletic persons. In addition stroke volume and cardiac output at rest was higher in endurance athletes than in athletes with static exercise and non-athletic persons. At rest no variations in parameters of heart muscle contractility related to heart size or sport-type could be detected.