One standard location for a pair of electrodes during an EKG is shown in the figure (Figure 1) . The potential difference ? V 31= V 3? V 1 is recorded.

For each of the three instants a, b, and c during the heart?s cycle shown in the figure A(Figure 2) , will ? V 31 be positive or negative? Explain.

1. 3. Atrial depolarization (b) Septal depolarization Ventricular depolarization 3.9