postcarga

Postcarga is a term used in physiology and cardiology to denote afterload—the pressure and resistance the heart must overcome to eject blood during systole. In Portuguese, postcarga and in many related vocabularies, it is synonymous with afterload. The left ventricle must generate enough pressure to exceed the aortic systolic pressure to open the aortic valve and propel blood into the aorta.

Determinants of postcarga include systemic vascular resistance, arterial pressure, and arterial compliance. An increase in these factors raises the afterload and the myocardial wall stress, increasing the work the heart must perform with each beat. Conversely, reduced vascular resistance or arterial pressure lowers afterload. Afterload is distinct from preload, which concerns ventricular filling, and from contractility, the intrinsic force-generating capacity of the myocardium.

Clinical relevance arises when afterload becomes chronically high, such as in hypertension or aortic stenosis, leading to greater ventricular workload, left ventricular hypertrophy, and potential heart failure. Low afterload, as seen in severe vasodilation or shock, can compromise perfusion. Afterload is not measured by a single simple value but is estimated from derived measurements such as arterial pressure, systemic vascular resistance, and metrics like end-systolic wall stress or effective arterial elastance.

Management focuses on reducing afterload when appropriate, often through vasodilator therapy (for example, ACE inhibitors, ARBs, nitrates, or hydralazine) and treatment of underlying hypertension or valvular disease. Understanding postcarga helps explain how vascular conditions influence cardiac performance.

See also: preload, contractility, left ventricle afterload.