In hypertrophic cardiomyopathy, the relation between left ventricular diastolic impairment and magnitude of left ventricular hypertrophy has not been clearly defined. In the present study, Doppler echocardiographic indexes of left ventricular diastolic filling were compared in 78 patients with hypertrophic cardiomyopathy and in 72 normal control subjects of similar age, and the relation between abnormalities of diastolic filling and magnitude of left ventricular hypertrophy was assessed. In patients with hypertrophic cardiomyopathy, isovolumic relaxation was prolonged (94 +/- 25 ms); peak early diastolic flow velocity (53 +/- 18 cm/s), deceleration of flow velocity in early diastole (341 +/- 142 cm/s2) and the ratio between early and late peaks of flow velocity (1.6 +/- 0.9) were reduced; and peak late diastolic flow velocity was increased (38 +/- 15 cm/s) compared with values in control subjects (76 +/- 12 ms, 65 +/- 12 cm/s, 512 +/- 131 cm/s2, 2.3 +/- 0.8 and 30 +/- 7 cm/s, respectively; p less than 0.001). Individual patient analysis showed that diastolic filling was abnormal in 52 (67%) of the 78 patients with hypertrophic cardiomyopathy. However, within the patient group, none of the Doppler diastolic indexes showed a significant correlation with maximal left ventricular wall thickness or the wall thickness index (correlation coefficients ranged from -0.15 to 0.10).(ABSTRACT TRUNCATED AT 250 WORDS)