Background and Aim: Characterization of penetrating intramyocardial coronary artery (PICA) flow in diseased myocardium may offer insight into the spectrum of coronary physiology. However, Coronary flow reserve (CFR) of PICA in apical hypertrophy(AH) has not been studied yet. This study was to test the feasibility of PICA-CFR measurement by using high-frequency transthoracic Doppler echo(TTE) and to evaluate the different hemodynamics and morphology of PICA in AH. Methods: In 50 subjects [mean age=57짹9 yrs ; M:F=27:23; 37 subjects without hypertrophy (Control), 9 with apical hypertrophy (AH), 4 with symmetrical hypertrophy(SH)] with normal coronary angiogram, we examined the myocardium just beneath the apical impulse window at a depth of 3 to 5 cm by using TTE (6- or 7-MHz centerline frequency transducer). After obtaining linear color signals of PICA using a special preset coronary program with a low Nyquist limit (12 to 20 cm), the width of color Doppler signal, peak (PDV) and mean (MDV) diastolic pulsed Doppler velocities and diastolic velocity time integrals (VTI) were measured. PICA-CFR was calculated as the ratio of hyperemic PDV after the intravenous infusion of adenosine (120 mg/kg/min) to baseline PDV. Width-ratio of PICA was calculated as the ratio of hyperemic to baseline width of color Doppler signal of PICA. Results: 1.We identified color flow Doppler signals and successfully measured PICA-CFR in 45(90%) of 50 subjects. 2. Baseline width of PICA was 1.29짹0.37 mm in AH, 0.83짹0.08 mm in SH and 1.06짹0.20 mm in Control (p=0.032 versus SH and Control). 3.PICA-CFR was 1.75짹0.48 in AH, 2.80짹0.59 in SH and 2.45짹0.70 in Control (p<0.05 versus SH and Control). 4.PICA-CFR was closely related to width ratio of PICA (r= 0.466, p=0.007). Conclusion: Measurement of PICA-CFR is feasible in a high percentage of subjects by using high-frequency TTE. AH has impaired PICA-CFR in spite of bigger diameter, that is related to decreased distensibility of PICA.