Myocardial distribution of coronary blood flow in the isolated supported heart preparation

The regional distribution of myocardial blood flow was studied by use of radioactive microspheres (15 micro-meters [mum]) under control conditions and during an intracoronary infusion of norepinephrine (2mug/min). In control experiments endocardial blood flow was generally greater than epicardial flow; during administration of norepinephrine the endocardium received significantly less blood flow. It is proposed that normally the endocardium is well perfused, but under conditions of stress, eg, norepinephrine infusion in the presence of a constant coronary blood flow, decreased endocardial blood flow results.