Right and left ventricular function was evaluated in 28 patients with dilated cardiomyopathy to determine whether both ventricular functions were equally impaired in each patient. The ejection fractions of both ventricles were measured using equilibrium radionuclide ventriculography. In 13 patients the left ventricular ejection fraction (LVEF) was lower than the right ventricular ejection fraction (RVEF) by 6% or more, their mean values being 24 +/- 8% (mean +/- SD) and 37 +/- 7%, respectively (group 1). The difference between the LVEF and RVEF was less than 6% in nine patients; LVEF 29 +/- 8% and RVEF 30 +/- 7% (group 2). In six patients the RVEF was lower than the LVEF by 6% or more, and their mean values were 21 +/- 6% and 37 +/- 10%, respectively (group 3). The frequency of ventricular tachycardia, which was determined by the Holter ECG, was significantly higher in group 3 (100%, 6/6) than in the others (group 1 + 2; 41%, 9/22), p less than 0.05. The NYHA functional class correlated well with the LVEF, but not with the RVEF. It was concluded that the left and right ventricular functions are not necessarily equally impaired in patients with dilated cardiomyopathy, and that the difference may correlate with their clinical features.