Schematic representation of the heart and normal cardiac electrical activity (intracellular recordings from areas indicated and eCg). hase SA node Slow response AV node Phase Fast Tricuspid Purkinje Resting potential response Ventricle Action potential phases 1: Early-fast repolarization 2: Plateau 3: Repolarization ECG ECGSchematic representation of the heart and normal cardiac electrical activity (intracellular recordings from areas indicated and ECG). Slow response Fast response ECG