We compared the pattern and reserve of coronary flow in 8 cases of hypertrophic non-obstructive cardiomyopathy (H) with those in 20 cases of chest pain not accompanied by organic heart disease (N). A catheter-tip Doppler velocimeter was positioned in the proximal portion of the left anterior descending (LAD), circumflex (LCX) and right coronary (RCA) arteries. Coronary flow velocity (Vs: systolic peak, Vd: diastolic peak, Vm: mean) was recorded and the area under the velocity curve was divided into systole (* s) and diastole (* d). The time interval between the dicrotic notch in aortic pressure and the peak of diastolic flow velocity was measured (Tpv). Vm was measured before and after intracoronary injection of 6 ml of contrast media, and peak to resting velocity ratio (PRVR) was calculated as an index of coronary flow reserve. RESULTS In LAD, N showed diastolic predominant coronary flow pattern without backward flow. In H, diastolic predominance was more prominent with systolic backward flow, resulting in decrease in * s/* d(H: 0.07 +/- 0.04, N: 0.25 +/- 0.02, p less than 0.01). In H, Vd (H: 20.1 +/- 2.8, N: 9.2 +/- 1.4 cm/sec, p less than 0.05) and Vm(H: 9.5 +/- 1.3, N: 4.9 +/- 0.7 cm/sec, p less than 0.05) were higher, while PRVR was lower (H: 1.7 +/- 0.1, N: 2.6 +/- 0.1, p less than 0.05). In both N and H, the flow pattern of LCX was diastolic predominant with two peaks (one in systole and the other in diastole).(ABSTRACT TRUNCATED AT 250 WORDS)