Increased susceptibility of the left ventricular subendocardium to ischemic injury has been demonstrated during a variety of physiologic maneuvers in both normal and hypertrophied hearts. Further studies of regional myocardial blood flow in hearts with left ventricular hypertrophy (LVH) and critical coronary artery stenosis has documented even greater degrees of ischemia. These studies were conducted on hearts with LVH secondary to chronically elevated ventricular afterload distal to the coronary ostia. The lack of a laboratory model of LVH secondary to aortic valve or subvalve stenosis has hindered complete investigation of regional myocardial blood flow in these settings. To elucidate this further, we are subjecting Newfoundland dogs with LV secondary to congenital discrete subaortic stenosis to different physiologic maneuvers after placing a critical stenosis on one major coronary artery. Regional myocardial blood flow is then measured using 9 plus or minus 1 micron radioactive microspheres.