Cardiac Output Can Increase Nearly Fourfold Without Greatly Increasing the Pulmonary Arterial Pressure

(From Guyton AC, Hall JE. Textbook of Medical Physiology. 10th ed. Philadelphia, PA: Saunders; 2000, with permission.)

The end diastolic and the end systolic pressure-volume relationships represent the boundaries for the loops. The width of the pressure-volume loop represents the stroke volume (SV). Increases or decreases in myocardial contractility make the end systolic pressure-volume relationship steeper or shallower. The four segments of the loop (isovolumic contraction, ejection, isovolumic relaxation, ventricular filling) for the left ventricle are depicted in succession by mitral valve closure (1), aortic valve opening (2), aortic valve closure (3), and mitral valve opening (4).