<prompt> Mechanism of digitalis in atrial fibrillation:Decrease in contractilityNa K ATP ase pump inhibitionIncrease refractoriness of AV nodeBradycardia  <response>: Ans. C. Increase refractoriness of AV nodeDigoxin is inotropic agent used in heart failure. It has positive inotropic effect and negative chronotropic effect. Inotropic effect is due to blockade of NaKATPase pump. Chronotropic effect is due to vagomimetic effect which increase the refractoriness of AV node. This mechanism is utilized in atrial flutter and fibrillation. Answer is C 