Unloading the heart in congestive heart failure.

Depressed contractile performance of the heart in congestive heart failure is aggravated by increases in preload and afterload related in part to arterial and venous constriction. Vasodilator drugs have a salutary effect on left ventricular performance by reducing aortic impedance and/or increasing venous capacitance resulting in an increase in stroke volume and a lowering of filling pressure. Vasodilators may act by counteracting the heightened neurohumoral vasoconstriction tone in heart failure (inhibition of the sympathetic nervous system, inhibition of the renin-angiotensin system) or by more directly affecting vascular smooth muscle tone (direct vasodilators, calcium antagonists). The immediate effects of these drugs on resting hemodynamics must be supplemented by knowledge of their effects on the circulatory response to exercise and of their efficacy during long-term administration before a rational choice can be made as to the ideal agent or combination of agents to use in the long-term management of congestive heart failure.