Atrium « Back to Glossary IndexEither one of the heart’s two upper chambers. Why not check out these other entries? Related Articles: Glossary: Atrial Septal Defect [ASD]Glossary: Mitral ValveGlossary: Mitral Valve ProlapseGlossary: Pulmonary VeinGlossary: Sinus Node [SA]« Back to Glossary Index