The purpose of the study was to analyse relationships between the presence and magnitude of a regurgitant wave from the left ventricle to the left atrium and the state of the pulmonary circulation in patients with primary dilated cardiomyopathy. The study population consisted of 97 patients divided into three subgroups I--41 patients without the regurgitant wave, II--31 patients with the first-degree regurgitant wave, III--25 patients with the second-degree regurgitant wave. Diagnosis was based upon non invasive studies, cardiac catheterization and left ventriculography. Average values of the left ventricular systolic and end-diastolic pressures were similar in all subgroups, whereas the cardiac index was the lowest in the subgroup of patients with a large regurgitant wave to the left atrium. There were no differences in mean values of the pulmonary artery pressures, total pulmonary resistance and pulmonary vascular resistance between the patients without the regurgitant wave (subgroup II). In contrast the patients with a large regurgitant wave (subgroup III) showed statistically significantly higher pulmonary artery pressures, higher total pulmonary resistance and pulmonary vascular resistance. In 64% of the patients of this subgroup the left atrium was said to be large. The results of the present study indicate that even not a large regurgitant wave (second-degree) from the left ventricle to the left atrium leads to secondary pulmonary hypertension in patients with primary dilated cardiomyopathy.