The effect of one intravenous dose of verapamil on left ventricular diastolic and systolic flow was studied by Doppler-echocardiography in 31 patients with hypertrophic cardiomyopathy. On diastolic flow, verapamil induced a decrease in "a" wave velocity (1.02 + 0.37 vs 0.91 + 0.29 m/seg, p less than 0.01), and in its relation with maximal protodiastolic velocity (1.08 + 0.56 vs 0.89 + 0.37, p less than 0.01), and a shortening in the isovolumic relaxation period (0.076 + 0.031 vs 0.068 + 0.02, p less than 0.05). On the ejection flow, verapamil decreased the peak velocity (2.82 + 1.28 vs 2.42 + 1.18 m/seg, p less than 0.001). Nor age, sex, ventricular mass, gradient, neither hypertrophic cardiomyopathy's classification relates with changes after intravenous verapamil. There were no adverse effects. This study by Doppler-echocardiography confirms the beneficial ++ effect of intravenous verapamil in patients with hypertrophic cardiomyopathy not only on gradient reduction but also in the improvement on left ventricular diastolic function.