**Core Concept:** The coronary sinus is a large vein that collects blood from the coronary arteries and returns it to the right atrium of the heart. Its tributaries are veins that branch off from it and carry blood to it.

**Why the Correct Answer is Right:** The correct answer, option D (the right coronary vein), is the tributary of the coronary sinus because it collects blood from the right coronary artery and brings it to the coronary sinus. The right coronary artery supplies blood to the right ventricle, right atrium, and part of the right ventricle's free wall. When this blood reaches the coronary sinus, it is mixed with blood from other coronary arteries before entering the right atrium.

**Why Each Wrong Option is Incorrect:**

A. Option A (the left coronary vein) is incorrect because the left coronary artery supplies blood to the left ventricle, left atrium, and part of the left ventricle's free wall. Thus, the left coronary vein wouldn't branch off from the coronary sinus, making it an incorrect answer.

B. Option B (the anterior interventricular vein) is not the right answer because it is a vein that drains blood from the anterior wall of the left ventricle. Since the question is about a tributary of the coronary sinus, the anterior interventricular vein is irrelevant.

C. Option C (the posterior interventricular vein) is not the correct answer because it drains blood from the posterior wall of the left ventricle. This vein is not part of the tributaries of the coronary sinus.

**Clinical Pearl:** Understanding the anatomy of the coronary sinus and its tributaries is essential for understanding cardiac circulation and surgical procedures, such as coronary artery bypass grafting (CABG), where the surgeon uses veins or arteries from other parts of the body to bypass obstructed coronary arteries and restore blood flow to the heart muscle.

**Correct Answer:** D. Right coronary vein

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**Core Concept:** The coronary sinus collects blood from the right coronary artery and other right coronary artery tributaries, which are veins draining blood from the right ventricle, right atrium, and part of the right ventricle's free wall. This blood is then mixed with blood from other coronary arteries before entering the right atrium.

**Why the Correct Answer is Right:** The right coronary artery supplies blood to the right ventricle, right atrium, and part of the right ventricle's free wall. The right coronary vein is the only vein that drains blood from these areas and, thus, is the correct answer.

**Why Other Options are Incorrect:**

A. The left coronary artery supplies blood to the left ventricle, left atrium, and part of the left ventricle's free wall. The anterior interventricular vein, posterior interventricular vein, and left coronary vein are veins that drain blood from the left ventricle and left atrium, making them irrelevant to the tributaries of the coronary sinus.

**Clinical Correlation:** Understanding the anatomy of the coronary sinus and its tributaries is essential for understanding cardiac