Procainamide differs from quinidine in the following respect (a) It does not cause paradoxical tachycardia (b) It has no alfa adrenergic blocking activity (c) It has little antivagal action (d) Both (b) and (c) Ans: D 68. In heart, potassium channels determine (a) Pacemaker function (b) Resting potential (c) Action potential duration (d) All of the above