Introduction

Abstract

To meet the metabolic requirements of the body over a wide range of physical activity, the heart must be capable of increasing its cardiac output seven-to eightfold. This is accomplished by acute increases in heart rate and stroke volume. The elevations in stroke volume are produced through coordinated adjustments to the cardiac, respiratory, and peripheral circulatory systems which result in 1) enhanced myocardial contractility, 2) decreased systemic vascular impedance (i.e., reduced afterload), and/or 3) increased venous return leading to larger ventricular diastolic volumes (i.e., increased preload).