Final answer:
The posterior interventricular sulcus is a groove on the heart that contains the posterior interventricular artery and the middle cardiac vein, which drains into the great cardiac vein and then into the right atrium.
Step-by-step explanation:
The posterior interventricular sulcus is a groove that is located on the heart's surface and lies between the left and right ventricles. It houses the posterior interventricular artery (also known as the posterior descending artery) and the middle cardiac vein. The middle cardiac vein drains the regions of the heart that are supplied by the posterior interventricular artery and eventually empties into the great cardiac vein, which then flows into the coronary sinus and ultimately into the right atrium. This system plays a critical role in the heart's coronary circulation, ensuring that deoxygenated blood is properly returned from the myocardium to be reoxygenated in the lungs.