Effect of increases in afterload before and after coronary occlusion in awake dogs

Ventricular function curves relating stroke work and left ventricular end-diastolic pressure were generated in awake dogs during increases in preload produced by infusion of fluid and during increases in afterload produced by administration of phenylephrine. The ventricular function curves produced by preloading were steeply upsloping whereas those produced by afterloading were essentially horizontal. Coronary occlusion produced downward displacement of these horizontal curves, but no change in slope. Thus increases in afterload did not help to demonstrate the functional impairment produced by coronary occlusion.