What is the pathway of blood flow through the heart?

Normal Pathway of Blood Flow Through the Heart

In the normal heart, deoxygenated blood returns from the body through the superior and inferior vena cava to the right atrium, passes through the tricuspid valve into the right ventricle, is pumped through the pulmonary valve into the pulmonary arteries to the lungs for oxygenation, returns via pulmonary veins to the left atrium, flows through the mitral valve into the left ventricle, and is ejected through the aortic valve into the aorta to supply the systemic circulation. 1, 2

Systemic Venous Return to Right Atrium

• Deoxygenated blood from the upper body travels through the superior vena cava (SVC) to reach the right atrium 3, 4
• Deoxygenated blood from the lower body travels through the inferior vena cava (IVC) to reach the right atrium 3, 5
• The right atrium combines these two venous streams, with the IVC typically contributing approximately 65% and the SVC contributing 35% of total venous return under normal physiologic conditions 4
• Blood flow in the vena cavae is highly helical as it enters the right atrium, creating a characteristic vortex pattern in the central right atrium 4

Right Heart Circulation

• Blood flows from the right atrium through the tricuspid valve into the right ventricle 1
• The tricuspid valve guards the right atrium and systemic veins from the pressure generated in the right ventricle 1
• The right ventricle acts as a pump that actively propels systemic venous blood into the pulmonary circulation 1
• Under normal conditions, central venous pressure remains low (less than 10 mmHg) while systolic pulmonary artery pressure is higher (greater than 15 mmHg) 1
• Blood is ejected from the right ventricle through the pulmonary valve into the pulmonary arteries 1

Pulmonary Circulation

• Blood flows through the pulmonary arteries to the lungs where gas exchange occurs at the alveolar-capillary membrane 2
• Low pulmonary vascular resistance allows efficient blood flow through the lungs with minimal cardiac work 2
• Oxygenated blood returns from the lungs via pulmonary veins to the left atrium 3, 6

Left Heart Circulation

• Blood flows from the left atrium through the mitral valve into the left ventricle 1
• The left ventricle, with its greater myocardial thickness and contractile power compared to the right ventricle, generates the pressure needed for systemic circulation 1
• Blood is ejected from the left ventricle through the aortic valve into the aorta 1
• The aorta distributes oxygenated blood to the entire body, completing the circuit 3

Key Physiological Principles

• The pulmonary and systemic circulations are connected in series, with each circulation supported by its own ventricle 1
• The volumes of the systemic venous return and pulmonary venous return are in balance in a normal physiologic state 3
• Cardiac output increases up to 6 times resting levels during exercise to meet increased oxygen demands, with blood diverted from non-active tissues to skeletal muscles 2
• The cardiovascular system provides blood flow while the pulmonary system enables gas exchange, working together to deliver oxygen to tissues and remove carbon dioxide 2