Representative activation maps showing normal impulse conduction across the ventricular epicardium of control hearts. The change in color represents time, with red indicating the earliest and purple the latest activation. A, Anterior view, right (RV) and left (LV) ventricles in view, apex (A) at the bottom. Note 2 breakthroughs (⋆) on the ventricular surface toward the apex of the heart. B, Representative vECG collected from a control heart. Atrial (P) and ventricular (QRS) depolarizations were clearly defined. C and D, Views from the posterior surface of the ventricle showing 2 types of normal activation patterns. Arrows show direction of impulse propagation. In C, the impulse wrapped around from the anterior surface. In D, breakthroughs occurred along the septal surface.