Effect of heart rate and intracoronary isoproterenol, levarterenol, and epinephrine on coronary flow and resistance.

TVFUMEROUS studies have been published •*• ^ on the effect of heart rate and various drugs on coronary flow. It has not been possible to estimate the relative importance of changes in intravaseular and extravascular resistance in determining the observed alterations in coronary flow. Recently, Sabiston and Gregg suggested that in a heart in which coronary arteries were perfused at constant pressure the immediate change in flow induced by vagal asystole was due to the removal of the extravascular resistance of the contracting myocardium. They found that coronary flow consistently rose and concluded that extravascular resistance acted to impede coronary flow. In the present experiments, a similar approach was used to determine the effect of changes in heart rate and of intracoronary epinephrine, norepinephrine, and isoproterenol on extravascular and intravaseular resistance.