This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
Digitalis has positive Inotropic effect-by the viue of its effect on: 
Select and explain. 
A. Na+K+ ATPase pump, B. Na Glucose channels, C. H+K+ ATPase pump, D. Calcium pump
A: Na+K+ ATPase pump
Answer: A: Na+K+ ATPase pump 
Explanation: Ref:KDT 6/e p496 Digitalis is used clinically because it exes a positive inotropic effect and because it slows transmission in the AV node in patients with supraventricular tachyarrhythmias. The positive inotropic effect is due to inhibition of the sodium/potassium pump at the outer cell membrane.