15 patients with cystic fibrosis aged 8-19 years were graduated into 3 stages of the cor pulmonale dependent on results of an examination with the microcatheter: stage 0:6, stage I: 4 and stage II: 5 patients. These patients were studied in the period from April 1987 to January 1988 echocardiographically. With this size and contractility of the right ventricle were especially considered. The end-diastolic and end-systolic area of the right ventricle could be measured in the apical 4-chamber-view in 14 of the altogether 15 patients and out of this the fractional area-shortening could be calculated. The end-diastolic area of the right ventricle in the patients with stage 0 was on an average 11.4 cm2/m2 body surface bs (8.7-13.5), in stage I 11.2 cm2/m2 bs (9.2-13.5), and in stage II 9.7 cm2/m2 bs (9.0-10.8). The end-systolic area of the right ventricle in stage 0: 7.2 cm2/m2 bs (6.8-8.4), stage I: 7.1 cm2/m2 bs (6.0-8.5), and stage II: 8.02 cm2/m2 bs (6.4-10.1). The results we found don't differ significantly in the 3 groups. Contrary to this fractional area-shortening of the right ventricle shows a falling tendency: stage 0.35.2% (22-49), stage I 32% (7-56), stage II 17.2% (4-38) with an increasing part of patients with a value under 28% (stage 0:1 patients, stage I 2 patients, stage II 3 patients). Contractility and pump-efficiency of the left ventricle were calculated in the apical 4-chamber-view according of the area-length-method. The findings don't show an increasing size of the right ventricle in the sense of a cor pulmonale but a decreasing contractility and pump-efficiency of the right ventricle as expressions of a cardial manifestation of the basic illness in the sense fo a symptomatic cardiomyopathy. A disturbance of the contractility of the left ventricle could be seen in 7 of the 15 patients (47%).