BACKGROUND: Hypertrophic cardiomyopathy (HCM) is thought to be associated with microvascular dysfunction. Stress-perfusion cardiovascular magnetic resonance imaging (CMR) is a sensitive method for assessing microvascular perfusion abnormalities. We evaluated the prevalence and clinical significance of adenosine-induced perfusion defects on CMR in patients with HCM. METHODS: One hundred and one subjects with hypertrophic cardiomyopathy underwent adenosine-stress perfusion CMR for evaluation of stress-induced perfusion defects. The perfusion defect was correlated with clinical characteristics, presence and extent of late Gadolinium enhancement (LGE) on CMR, left ventricular (LV) mass index and volume, abnormalities on 24-hour ECG monitoring and treadmill exercise tests. RESULTS: The mean age of the patients was 54.3짹11.6 years and gender ratio was M:F=86:15. LGE was present in 88 (87.1%) subjects. Apical aneurysm was found in 12 (11.9%) subjects. Stress-induced perfusion defects were present in 56 (55.4%) subjects, and LGE in the myocardium was present in all but one of them. The defect was independently associated with higher LV mass index (P = 0.02), presence of LGE (P = 0.002), higher LGE volume and proportion (P = 0.02 and 0.005, respectively), presence of apical aneurysm (P < 0.001), and inadequate blood pressure response to exercise (P = 0.048) by multivariate analysis. CONCLUSIONS: In patients with HCM, adenosine-induced perfusion defects on CMR are relatively common findings present in more than 50%. The perfusion defect is associated with higher LV mass index, presence and extent of LGE, apical aneurysm, and inadequate hemodynamic response to exercise. The prognostic value of this finding needs further elucidation.