Stroke volume is defined as end-diastolic volume minus end-systolic volume; cardiac output is the stroke volume times the heart rate. The left ventricular pressure–volume loop is drawn and the work of the heart is considered as the area within the loop. Total cardiac work, however, includes the kinetic work, PV work, and gravitational work. The stretch of the heart caused by the preload determines the stroke volume. This becomes the Frank–Starling Law of the Heart. The plot of cardiac output against right atrial pressure is considered to be the cardiac function curve. The effect of afterload and preload on the PV loop is considered. The effect of sympathetic stimulation on the left ventricular pressures and the PV loop is shown. Experimental determination of cardiac output by Fick’s principle and the indicator dilution method are discussed.