Deoxygenated blood from the body returns to the right atrium of the heart via the superior and inferior vena cava. From the right atrium, the blood flows into the right ventricle, passing through the tricuspid valve, which prevents backflow. The right ventricle then pumps the blood to the lungs for oxygenation through the pulmonary artery.

Once oxygenated, the blood returns to the heart via the pulmonary vein, entering the left atrium. From there, it is pumped into the left ventricle, the final chamber of the heart. The left ventricular wall is thick and muscular, allowing it to generate the force needed to pump oxygen-rich blood through the aorta and distribute it to the rest of the body.

he process of cardiac excitation begins with the sinoatrial (SA) node, which generates an action potential (excitation signal). This signal propagates across the atria, triggering their contraction. Upon reaching the atrioventricular (AV) node, the signal experiences a brief delay, allowing the atria to contract before the ventricles are stimulated fully. From the AV node, the excitation is transmitted to His bundle, which runs along the interventricular septum. The bundle of His branches into Purkinje fibres, which distribute the signal throughout the ventricles, causing them to contract and effectively pump blood.