BACKGROUND: Left ventricular hypertrophy (LVH) has often been supposed to be associated with abnormal myocardial blood flow and resistance. The aim of this study was to evaluate and quantify the physiological and pathological changes in myocar-dial blood flow and microcirculatory resistance in patients with and without LVH attributable to severe aortic stenosis. METHODS AND RESULTS: Absolute coronary blood flow and microvascular resistance were measured using a novel technique with continuous thermodilution and infusion of saline. In addition, myocardial mass was assessed with cardiac magnetic resonance imaging. Fifty-three patients with aortic valve stenosis were enrolled in the study. In 32 patients with LVH, hyper-emic blood flow per gram of tissue was significantly decreased compared with 21 patients without LVH (1.26±0.48 versus 1.66±0.65 mL·min^{−1·g −1}; P=0.018), whereas minimal resistance indexed for left ventricular mass was significantly increased in patients with LVH (63 [47– 82] versus 43 [35– 63] Wood Units·kg; P=0.014). CONCLUSIONS: Patients with LVH attributable to severe aortic stenosis had lower hyperemic blood flow per gram of myocar-dium and higher minimal myocardial resistance compared with patients without LVH.