Seventeen patients with dilated cardiomyopathy (mean ejection fraction 22%) in the NYHA state III or IV were investigated. All patients fulfilled the criteria of an indication for administration of furosemide, since left ventricular filling pressure (LVFP, measured as pulmonary capillary pressure) was 20 or more mm Hg in all. This study investigates the effects of an acute (40 mg i.v.) administration of furosemide (observation period 0 to 90 minutes after administration). Conventional M-mode, 2-dimensional and Doppler-echocardiography was performed in all patients. Patients were divided into 2 groups according to the degree of (relative) mitral regurgitation (MR): group 1 with moderate to severe (n = 10) and group 2 with mild or no MR (n = 7), 90 minutes after administration of furosemide LVFP decreased by 76%. In group 1 this occurred together with a 23% rise of cardiac index and a fall of systemic vascular resistance of 21%. In group 2 cardiac index decreased by 22% with a rise of systemic vascular resistance of 14%. The chronic oral administration of furosemide over 4 weeks ameliorated the NYHA state of all patients by one grade. We conclude from our results that patients with advanced dilated cardiomyopathy profit only from acute administration of furosemide if a significant (relative) MR is present also. A low dose chronic oral administration of the drug, however, leads in any case to clinical amelioration.