DICKHUTH, H.-H., T. HORSTMANN, J. STAIGER, H. REINDELL, and J. KEUL. The long-term involution of physiological cardiomegaly and cardiac hypertrophy.Med. Sci. Sports Exerc., Vol. 21, No. 3, pp. 244–249, 1989. Forty-five former athletes in endurance disciplines, primarily Olympic medalists and World Cup, European Cup, and German champions, for whom results of an exercise ECG and radiological heart volume measurement were available from their active competitive phase, were examined. The study protocol included clinical examination, laboratory controls, resting and exercise ECG, determination of cardiac volume, and one- and two-dimensional echocardiographic examination. Of the 45 former athletes contacted, 38 appeared for examination. Of these, four presented with heart disease (two with infarction, one with aortic stenosis, and one with arrhythmia). The remaining 34 were divided into groups of still active (more than 300 kcal·wk-1) and inactive (less than 300 kcal·wk-1) athletes. The interval between the first and second examination averaged 23 yr. The active former athletes showed a weight increase of 5.2% (P< 0.01) and a reduction of 14% in ergometric performance (P< 0.02). The inactive group had a marked weight increase of 17.4% (P< 0.001); the ergometric performance was lowered by 20% (P< 0.001). The absolute heart size had decreased in the active group by 6.1 % (NS) and the relative heart size by 10.7% (P< 0.005); the corresponding values in the inactive group were 4.5% (NS) and 18% (P< 0.001). The echocardiographic data showed an elevated end-diastolic volume and an increased muscle mass in the active group (164 ± 19 ml; 173 ± 34 g) compared to the inactive group (148 ± 25 ml; 155 ± 21 g) and a control group (140 ± 20 ml; 148 ± 25 g). The inactive group differed only slightly from the control group. Former athletes do not appear to develop cardiac diseases more frequently than non-athletes. Over time involution of heart size and cardiac hypertrophy, as well as physical exercise capacity, occurs in relation to the activity level maintained but is not completely even in inactive individuals. Even slight training stimuli appear to maintain the structural and functional adaptation processes. Genetic factors and an incomplete regression capacity are discussed in this respect.