The coronary sinus, the primary venous drainage of the heart, opens into which cardiac chamber and is guarded by which valve?

• A Right ventricle, guarded by the Eustachian valve
• B Right atrium, guarded by the Thebesian valve ✓
• C Left atrium, guarded by no valve
• D Right atrium, guarded by the Eustachian valve

Explanation

The coronary sinus opens into the right atrium at the junction of the right atrium and inferior vena cava, between the IVC orifice and the tricuspid valve. It is guarded by the valve of the coronary sinus (Thebesian valve), a semi-lunar fold that prevents backflow during atrial systole. The Eustachian valve (valve of the IVC) guards the IVC orifice and, in fetal circulation, directs oxygenated blood from the IVC through the foramen ovale.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.