To analyze right-ventricular size and function and their relationship to left-ventricular dimensions in patients with dilated cardiomyopathy (DCM), biplane cineventriculography was performed in 57 patients. The results were compared to 15 normals (N). In patients dilatation of the right ventricle (RVEDVI: DCM: 126.5 +/- 41.4 ml/m2, N: 90.5 +/- 9.2 ml/m2, 2 p < 0.05) was less pronounced than dilatation of the left ventricle (LVEDVI: DCM: 136.0 +/- 45.8 ml/m2, N: 76.7 +/- 7.9 ml/m2, 2 p < 0.05). Left-ventricular ejection fraction (LVEF: DCM: 36.1 +/- 10.2 %, N: 64.4 +/- 3.8 %, 2 p < 0.05) was more reduced than right-ventricular ejection fraction (RVEF: DCM: 39.7 +/- 11.5 %, N: 58.3 +/- 3.3 %, 2 p < 0.05). Concerning the individual patient, a good correlation was found between right- and left-ventricular stroke volume (r = 0.74), whereas ejection fraction (r = 0.58), enddiastolic (r = 0.52) and endsystolic volume (r = 0.55) of the left and right ventricle correlated only moderately. Twenty-three of the 57 patients showed pronounced differences between right- and left-ventricular ejection fraction. The difference RVEF-LVEF was < = -10% in six patients, i.e., right-ventricular ejection fraction was markedly more reduced than left-ventricular ejection fraction. Right-ventricular myocardial biopsy was performed in five of these six patients with histologic evidence of dilated cardiomyopathy and, also, no signs of right-ventricular dysplasia (no lipomatous tissue replacement). The difference RVEF-LVEF was > = + 10 % in 17 patients. Secondly, the degree of dilatation of both ventricles differed markedly in 26 patients (difference LVEDVI-RVEDVI < = -25 ml/m2, or > = +25 ml/m2. Thus, the cardiomyopathic process may predominantly affect the right or the left ventricle as well.