Changes in left ventricular systolic and diastolic function and outflow gradient were evaluated in patients with obstructive hypertrophic cardiomyopathy after intravenous acute treatment with verapamil (15 patients) and after six months of oral chronic treatment (11 patients). All patients had severe symptoms despite beta blockade, and the condition of all but two improved appreciably after chronic treatment with verapamil. Resting left ventricular outflow tract gradient decreased in six of 15 patients after intravenous verapamil, and in five of 11 patients after long term treatment, but there was no change in provocable gradients nor any correlation between changes in gradient and improvement in symptoms. Left ventricular ejection rate did not change after intravenous or oral treatment. End systolic pressure/end systolic volume index remained unchanged after oral verapamil treatment. Whereas left ventricular total stroke volume index and end diastolic volume index increased without any significant change in left ventricular end diastolic pressure, indicating improved left ventricular diastolic function. In some patients the left ventricular diastolic pressure-volume curve shifted downwards or to the right or both. These findings suggest that improvement in symptoms with verapamil in patients with obstructive hypertrophic cardiomyopathy is unlikely to be related to changes in left ventricular outflow gradient or in systolic function and may be related to improved diastolic function.