To determine the relationship of left ventricular function and ventricular tachycardia, 48 hour ECG monitoring and technetium-99m gated equilibrium radionuclide angiography were performed in 84 consecutive patients with hypertrophic cardiomyopathy and sinus rhythm. Measurements of ejection fraction (EF), peak ejection rate (PER, edv/s), peak filling rate (PFR, edv/s) and time to peak filling rate (PFR, ms) were derived from radionuclide activity time curves generated from data acquired in list-mode. Left ventricular function was compared in patients with and without ventricular tachycardia. Left ventricular ejection fraction was significantly lower in 16 patients with ventricular tachycardia compared to 68 patients without (67 +/- 17 vs 78 +/- 10, P less than 0.05) and time to peak filling rate was significantly prolonged (152 +/- 32 vs 120 +/- 36, P less than 0.05). Thus patients with hypertrophic cardiomyopathy at greatest risk of sudden death had significant impairment of systolic and diastolic left ventricular function.