Regular exercise training modifies the morphological and functional properties as well as the autonomous regulation of the heart. Such changes constitute what is termed an athletic heart, and were found to be reversible so after a discontinuation of regular exercise cardiac parameters gradually return to the non-athletic values. As yet, however, it has not been fully settled 1) how long a period of detraining is necessary to elicit such reversion, and 2) whether the various characteristics of an athletic heart would move concurrently or the time course of their change is different. In order to get more insight, the echocardiographic correlates of these problems were studied in 22 female and 23 male physical education students forced by an injury to discontinue their exercise for some time. A sex and age matched group of non-athletic subjects and data published about a group of elite athletes served as contrast. The studied resting parameters were the wall thickness and internal diameter of the left ventricle, left ventricular relative muscle mass, relative stroke volume and cardiac output, and heart rate. It was inferred that--in respect of the echographical parameters--the time taken until the first signs of detraining depended on the athlete's previously attained level of conditioning, and that there was a definite order of sequence in that functional changes preceded morphological ones.