CVS Practice Test

What structure in the right atrium protects the entrance of the coronary sinus?

1. Eustachian valve

2. Tricuspid valve

3. Mitral valve

4. Pulmonary valve

The correct answer is: Eustachian valve

The Eustachian valve is the structure located in the right atrium that serves to protect the entrance of the coronary sinus, which is the vessel responsible for draining blood from the heart muscle into the right atrium. This valve plays a role during embryonic development by channeling blood flow from the inferior vena cava toward the foramen ovale, which is essential for fetal circulation. After birth, its function diminishes, but it still remains as a flap of tissue that can prevent blood from flowing backwards into the coronary sinus during atrial contraction. In contrast, the tricuspid valve is primarily involved in regulating blood flow between the right atrium and right ventricle, the mitral valve serves a similar function on the left side of the heart between the left atrium and left ventricle, and the pulmonary valve controls blood flow from the right ventricle into the pulmonary artery. These valves are all essential for the overall circulatory function of the heart, but do not specifically guard the entrance of the coronary sinus in the right atrium.