What is the primary hemodynamic effect of digoxin on the heart?

• A. Increases heart rate
• B. Widen pulse pressure
• C. Decrease myocardial contraction
• D. Slows heart rate to improve filling and increase contraction

Answer: (D)

Digoxin works by two main actions on the heart. First, it increases the force of contraction (positive inotropy) by inhibiting the Na+/K+-ATPase in cardiac cells. This raises intracellular calcium via reduced activity of the Na+/Ca2+ exchanger, so each heartbeat squeezes more effectively. Second, it enhances vagal (parasympathetic) tone, which slows conduction through the AV node and lowers the heart rate. The combination—slower rate to allow longer filling time and stronger contraction to push out more blood—best describes the primary hemodynamic effect. It does not increase heart rate, does not widen pulse pressure as a primary effect, and does not decrease contraction.