Hemodynamic evaluation of a vasodilator drug is a difficult exercise in which Doppler echocardiography can be a useful tool. We studied the hemodynamic effect of isosorbide dinitrate (ISDN) by Doppler echocardiography in 7 patients with severe cardiac failure despite prolonged therapy with usually effective doses of captopril. The patients were evaluated before (H0) and 24 hours after treatment by ISDN (120 mg/24 hr) (H24) and 10 minutes after sublingual 0.75 mg of trinitrin (H24 + T). M mode echocardiography did not show any significant changes in chamber dimension as reported after vasodilator therapy in patients without cardiac dilation: in patients with severe left ventricular dilatation a reduction in LV filling pressures causes little if any changes in fractional shortening and ventricular dimensions. Two-dimensional echocardiography showed a reduction in end systolic volume and an increase in ejection fraction, emphasizing the superiority of this technique in cases of abnormal left ventricular function and the sensitivity of indices of systolic function to changes in afterload in these patients. Cardiac output measured by Doppler increased during the study. The maximal acceleration did not change significantly and pulmonary artery pressures were stable after administration of nitrates. ISDN caused a marked change in diastolic mitral flow patterns for which there are several explanations: an effect of ISDN on relaxation or LV compliance or on the conditions of LV filling or on both factors together. The presence of mitral regurgitation and/or atrial arrhythmia prevents the use of Doppler indices for analysis of diastolic LV function.(ABSTRACT TRUNCATED AT 250 WORDS)