16th February 2024

Cardiac anatomy

The heart consists of four chambers: two atria and two ventricles. The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava and pumps into the right ventricle through the tricuspid valve. The right ventricle then pumps this blood through the pulmonary trunk into the pulmonary circulation for oxygenation, and the oxygenated blood is returned via the pulmonary veins into the left atrium. 

Blood flows from the left atrium through the mitral valve into the left ventricle. Then, this oxygenated blood is supplied to the body, starting from the aorta to arteries, arterioles and the capillaries. The atria contract, and the AV valves (mitral and tricuspid) open in diastole. The ventricles contract, and outlet valves (Pulmonic and aortic) open in systole.

The heart’s conduction system begins at the sinoatrial node within the right atrial wall. The pacemaker cells spontaneously generate an electrical impulse, and these travel across the atrial walls. The impulses arrive at the atrioventricular (AV) node within the atrioventricular wall septum close to the coronary sinus. The impulses will travel from the AV node into the atrioventricular bundle (Bundle of His). The AV bundle will divide into the left and right bundle branches to supply the left and right ventricles. These bundles terminate as the Purkinje fibres as the electrical impulses are transmitted across the ventricular walls. 

Image Source: Wikimedia Commons (2015). Cardiac conduction system, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/3/3d/Cardiac_conduction_system.jpg (Accessed: 9 January 2024).