Which statement describes milrinone’s mechanism as used in HF?

• A. Milrinone decreases contractility.
• B. Milrinone blocks ACE.
• C. Milrinone is a PDE-3 inhibitor that increases cAMP, causing inotropy and vasodilation.
• D. Milrinone inhibits beta receptors.

Answer: (C)

Milrinone works by inhibiting phosphodiesterase-3, which prevents the breakdown of cAMP in cardiac and vascular smooth muscle. With higher cAMP levels, the heart increases calcium availability during systole, producing a stronger contraction (positive inotropy). At the same time, increased cAMP in vascular smooth muscle causes relaxation, leading to vasodilation and lower afterload. This combination improves cardiac output and reduces filling pressures in heart failure. It’s not an ACE blocker, not a beta-blocker, and it does not decrease contractility; it increases it along with vasodilation.