Vulnerability of the subendocardium to ischemic injury has been documented during a variety of physiologic conditions in animals with normal hearts and those with left ventricular hypertrophy secondary to chronically elevated afterload distal to the coronary arteries. However, the lack of a laboratory model for left ventricular hypertrophy with aortic valve or subvalvular stenosis has restricted investigation of regional myocardial blood flow in this setting. To study this, we subjected Newfoundland dogs with congenital discrete subaortic stenosis and left ventricular hypertrophy to a variety of hemodynamic alterations while measuring regional myocardial blood flow with radioactive microspheres.