We aimed to visualize the coronary flow velocities (CFV) of patients with hypertrophic obstructive cardiomyopathy by using transthoracic Doppler echocardiography, and to determine the relationship between abnormal CFV patterns and conventional echocardiography indices. Guided by 2-dimensional echocardiography and Doppler color flow mapping, CFV in the distal left anterior descending coronary artery were measured in 21 patients with hypertrophic obstructive cardiomyopathy using a 3.5-MHz transducer. The results were compared with those of 18 control subjects. Abnormal systolic flow patterns were observed in 15 (71%) patients (11 systolic-reversal flow and 4 no systolic flow). For patients and control subjects, peak diastolic velocity and velocity-time integral obtained from distal left anterior descending coronary artery were higher (63 ± 21 cm/s and 18.5 ± 4 cm vs 41 ± 11 cm/s and 14.2 ± 5 cm, respectively; P < .01 for both) whereas peak systolic velocity and velocity-time integral were significantly lower (−17 ± 10 cm/s and 4.5 ± 6 cm vs 24 ± 9 cm/s and 9.5 ± 4 cm, respectively; P < .001 for both). Significant positive and negative correlations between diastolic CFV and septal thickness index (r = 0.79, P < .0001), and between systolic CFV and septal thickness index (r = −0.65, P < .005), have been observed. CFV abnormalities that could easily be recorded by a standard Doppler echocardiographic study seem to be related to septal thickness rather than the degree of obstruction in hypertrophic obstructive cardiomyopathy.