<prompt> Mechanism of action of digitalis in atrial fibrillation is:By decreasing cardiac contractilityNa K ATPase inhibitionIncrease in refractoriness of AV nodal tissueBy causing bradycardia  <response>: Digoxin reduces ventricular rate in A. Fib. by decreasing the number of impulses that are able to pass down the A-V node and bundle of His. It increases ERP of A-V node by direct, vagomimetic and antiadrenergic actions -- Minimum interval between consecutive impulses that can successfully traverse the conducting tissue is prolonged. 