Before and 90 min. after the administration of prazosin(3mg p.o.), M-mode echocardiograms of left ventricle were recorded, from which end-diastolic and end-systolic dimensions of left ventricle and left ventricular ejection time were measured. Hemodynamic parameters of left ventricular performance, i.e., mean veloity of circumferential fiber shortening, fractional fiber shortening, ejection fraction, stroke volume, and cardiac output were calculated from the measurements.

Left ventricular end-diastolic and end-systolic dimensions were decreased significantly after prazosin administration and left ventricular performance was significantly increased after prazosin administration, whereas stroke volume was not. Total systemic peripheral resistance and mean arterial pressure showed no significant changes.

All cases, except one of the patients showed marked symptomatic relief after prazosin administration evaluated by NYHA functional classification.

There was no considerable untoward effect in the patients of congestive heart failure to whom the prazosin was administered.