Previous observations suggest the presence of ischemia in the disproportionately thickened interventricular septum (IVS) of patients with hypertrophic cardiomyopathy (HCM), although the details remain obscure. Utilizing digital subtraction coronary angiography (DSA) with LAO projection before and after intracoronary papaverine (P) injection, we evaluated regional myocardial coronary blood flow reserve (rMFR) consecutively 18 patients with HCM, and compared it with that of 8 patients without apparent cardiac abnormality (C). Time-density curves were obtained from digital angiograms of the myocardial region of interest. We measured peak contrast density (Cm) and time to peak contrast (Tm). An index of rMFR was calculated as the quotient of Cm/Tm before and after P. In HCM, rMFR in IVS and apex was significantly lower than that of C (Mid-IVS: 1.9 +/- 0.5 vs 3.9 +/- 0.5, p less than 0.001; Low-IVS: 2.0 +/- 0.5 vs 4.4 +/- 0.9, p less than 0.001; Apex: 2.0 +/- 0.7 vs 4.5 +/- 1.6, p less than 0.01). There was correlation between the impairment of rMFR and the extent of hypertrophy in HCM. In conclusion, we could state that, in HCM, the region of impaired myocardial coronary blood flow reserve is localized. In HCM, DSA is useful in evaluating myocardial coronary blood flow reserve.