Heart Chambers and Blood Flow: A Step‑by‑Step Guide

The heart is a four‑chambered dual pump that separates systemic and pulmonary circulations. Deoxygenated and oxygenated blood never mix in a healthy adult.

Chambers & Valves

Chamber	Receives	Pumps To	Outlet Valve
Right Atrium (RA)	SVC, IVC, Coronary Sinus (deoxygenated)	Right Ventricle	Tricuspid
Right Ventricle (RV)	Right Atrium	Pulmonary Artery	Pulmonic
Left Atrium (LA)	4 Pulmonary Veins (oxygenated)	Left Ventricle	Mitral
Left Ventricle (LV)	Left Atrium	Aorta	Aortic

Circulatory Pathway (One Cardiac Cycle)

1. Systemic venous return → SVC/IVC → RA.
2. RA contracts → blood crosses tricuspid → RV.
3. RV contracts → pulmonic valve opens → pulmonary artery → lungs (O₂ uptake, CO₂ release).
4. Oxygenated blood → 4 pulmonary veins → LA.
5. LA contracts → mitral valve → LV.
6. LV contracts → aortic valve → aorta → systemic arteries → capillaries → tissues.
7. Deoxygenated blood → systemic veins → back to step 1.

Electrical Conduction (Coordination)

• SA node (RA) – primary pacemaker (60–100 bpm).
• AV node – delays impulse (~120 ms) allowing atrial kick.
• Bundle of His → bundle branches → Purkinje fibers – rapid ventricular depolarization (apex → base).

Clinical Pearls

• LV wall ~3× thicker than RV (systemic vs. pulmonary pressure).
• Coronary arteries arise from aortic sinuses; perfusion occurs mainly in diastole.
• Shunts (ASD, VSD, PDA) allow mixing; fetal circulation uses foramen ovale & ductus arteriosus.