ABSTRACT
Ventricular function is best understood after studying heart muscle function. Preload, contractility, and afterload are the major determinants of ventricular function and are functional parameters based on ventricular myocyte mechanical properties. The volume of ventricular ejection, the stroke volume, is partly determined by the amount of preceding diastolic filling. Ventricular pressure and volume during the cardiac cycle can be plotted to create a pressure-volume loop. Pressure-volume loops are useful to evaluate ventricular function and the area of the loop is a measure of ventricular work. The afterload is the load on a ventricle during contraction. It is called "afterload" because it is the load on the ventricles after contraction begins. A precise measure of ventricular afterload involves measuring ventricular wall stress or force, since wall force is what myocytes must work with during pressure development and shortening. Normal left ventricular afterload increases with increases in aortic systolic blood pressure.
