The effects of coronary perfusion on ventricular function have been studied in isolated ventricle preparations working under different conditions. Coronary flow, oxygen consumption, ventricular stroke work, rate of ventricular pressure change during isovolumetric contraction (dPC), and diastolic ventricular pressure (DVPm) and pressure/inflow ratio were determined. Maintenance of coronary flow and oxygen consumption in 5 experiments did not prevent irreversible changes in DVPm, stroke work, and dPC when the right ventricle was acutely overloaded. These ventricles did not accumulate water. Decreasing coronary perfusion pressure at constant arterial oxygen content in 11 experiments led to inconsistent changes in DVPm, stroke work and dPC. Decreasing arterial oxygen content at constant coronary perfusion pressure in 10 experiments led to increased DVPm but inconsistent changes in stroke work and dPC. There was an inverse relationship between DVPm and oxygen consumption in the variable perfusion experiments, but not in the overloading experiments. Ventricular function did not change significantly with time in 6 experiments in which the conditions of workload and coronary perfusion were kept constant. It was concluded that irreversible changes in performance of acutely overloaded ventricles could be independent of coronary flow, myocardial water content, or duration of experiment.

Effects of work loads imposed at various times in the cardiac cycle were studied in isolated left ventricle preparations of dog hearts. In six preparations, resistance loads were applied briefly at times in ventricular systole; in six, volume loads were applied briefly at times in ventricular diastole; in six, experimental aortic regurgitation was produced. Simultaneous recorc1s of left ventricular and aortic pressures and electrocardiograms were used to cletermilie the subdivisions of the cardiac cycle and to measure the rates of isometric contraction and relaxation for evaluation of changes in ventricular contractility. The results of many observations indicated that the rates of isometric ventricular contraction and relaxation were not fixed by prior events, that contraction and relaxation could be altered independently, and that aortic regurgitation loaded the left ventricle at a time critical for its relaxation. Accommodation to aortic regurgitation included maintenance of contractility without diastolic left ventricular pressure rise; failure of accommodation was characterized by loss of contractility at high diastolic ventricular pressure.