Duration of the phases of left ventricular systole.

• The influence of heniodynamic variables on the duration of certain phases of ventricular systole has been studied by several investigators in intact animals and in isolated heart preparations.' Even in isolated hearts, it is not possible to change one heniodynainic variable without inducing changes in one or more intrinsic determinants of the heart's performance. For example, augmenting stroke volume at constant aortic pressure increases ventricular end-diastolic pressure and fiber length. Similarly, changes of aortic pressure or heart rate are each accompanied by adjustments of myocardial contractility. We felt, however, that a systematic analysis of the effects of changing selected hemodynamic variables on the duration of each phase of left ventricular systole might help to characterize further the intrinsic mechanisms of cardiac adaptation. This report describes the effects of altering separately stroke volume, mean aortic pressure and heart rate on the duration of left ventricular isovolumic contraction, ejection and total systole. The effects of digitalization and norepiuephrine infusion are also described.