Background Patients with hypertrophic cardiomyopathy (HCM) sometimes develop subendocardial ischemia (SEI) in the left ventricle (LV). In the present study it was examined whether volumetric variables obtained by gated single-photon emission computed tomography (SPECT) are useful in detecting exercise-induced SEI in patients with HCM. Methods and Results Exercise ^99mTc-tetrofosmin myocardial scintigraphy was performed in 26 HCM patients having non-obstruction and mild hypertrophy with a ventricular septal thickness ≤20 mm. SEI was quantified using software developed previously, and the results were correlated with volumetric variables obtained using Quantitative Gated SPECT software. Exercise-induced percentage change in LV end-systolic volume was higher in 9 HCM patients with SEI (25.8±3.1%) than in 17 patients without (10.0±2.5%, p=0.009), although the percentage change in LV end-diastolic volume was similar in the 2 groups. The receiver-operator characteristics curve of the percentage changes in LV end-systolic volume for the detection of SEI showed that the optimal cutoff was 17%. This cutoff point yielded a good diagnostic value for the presence of SEI with a sensitivity of 89%, specificity 82%, and likelihood ratio 5.04. Conclusions Gated SPECT technique is useful in detecting SEI during exercise in a select population of HCM patients. (Circ J 2007; 71: 256 - 260)