Blood flow was simulated in patients (Wilson et al. 1988) with physiologically significant coronary lesions (minimal lesion size dm = 0.95 mm; 68% mean diameter stenosis; measured coronary flow reserve (CFR) of 2.3) by using computational hemodynamics. Computed mean pressure gradients were about 9 mm Hg for basal flow, and flow limiting values about ∼ 35 mm Hg. Mean hyperemic flow rates were about 115 ml/min, and distal mean coronary pressures ∼ 55 mm Hg, a level known to cause ischemia in the subendocardium (Brown et al. 1984), and consistent with the occurrence of angina in the patients.