What compounds enhance cardiac contractility by inhibiting the Na+/K+ ATPase pump?

Cardiac glycosides are compounds that enhance cardiac contractility primarily by inhibiting the Na+/K+ ATPase pump. This inhibition leads to an increase in intracellular sodium concentrations, which indirectly promotes calcium influx through the sodium-calcium exchanger. As a result, the availability of calcium for contraction increases, thereby enhancing the force of cardiac muscle contraction or inotropic effect.

In contrast, the other compounds listed have different mechanisms of action. Beta blockers reduce the heart rate and cardiac output by blocking adrenergic receptors, which do not directly increase contractility. Calcium channel blockers inhibit the influx of calcium into cardiac cells, which may decrease contractility rather than enhance it. ACE inhibitors work to lower blood pressure and decrease cardiac workload by inhibiting the angiotensin-converting enzyme, but they do not directly affect the Na+/K+ ATPase pump or enhance contractility. Therefore, cardiac glycosides are uniquely effective in their role of increasing cardiac contractility by targeting the Na+/K+ ATPase pump specifically.