Pimobendan used in canine heart failure primarily acts as what?

• A. A diuretic that reduces preload.
• B. A beta blocker reducing heart rate.
• C. A positive inotrope and vasodilator.
• D. An ACE inhibitor reducing afterload.

Answer: (C)

Pimobendan primarily acts as a positive inotrope and vasodilator. It strengthens the heart's contraction by sensitizing the cardiac muscle to calcium, so each beat contracts more forcefully without raising intracellular calcium to harmful levels. At the same time, it inhibits phosphodiesterase-III in vascular smooth muscle, raising cAMP and causing vasodilation. The combination improves cardiac output while reducing afterload, which helps dogs with heart failure. It is not a diuretic (which would mainly reduce preload by fluid removal), not a beta blocker (which would lower heart rate and contractility), and not an ACE inhibitor (which lowers afterload through RAAS blockade).