A patient is having electrical conduction blocks in the posterior surface of the right atrium. This condition leads to irregular heartbeats. To treat this condition, a cardiologist must insert electrodes into the posterior surface of the right atrium and destroy the affected area. She has to navigate through the venous system to reach the posterior surface of the right atrium. Once past the coronary sinus, which vein must she traverse?
A. Anterior cardiac vein
B. Small cardiac vein
C. Great cardiac vein
D. Middle cardiac vein