Pathophysiology. The end result of all types of heart failure is insufficient cardiac output. The loss of forward flow (cardiac output) causes a decrease in perfusion to the kidneys and the release of renin. Renin converts angiotensin l to angiotensin ll, a potent vasoconstrictor. The vasoconstriction increases the resistance (afterload) that the heart must pump against. Angiotensin II also stimulates the release of aldosterone, which causes the kidneys to retain sodium and water. This increases the circulating volume (preload) and contributes to volume overload.