How the Heart Works

Located between the lungs, the heart muscle continuously pumps blood to deliver oxygen and nutrients to the body’s vital organs, cells and tissues. The human heart is made up of four chambers:

• Right atrium: The right atrium receives non-oxygenated blood from the superior vena cava and inferior vena cava. The blood is then pumped through the tricuspid valve and into the right ventricle.
• Right ventricle: The right ventricle pumps blood through the pulmonary valve into the lungs, where it is oxygenated.
• Left atrium: The left atrium receives the oxygenated blood from the lungs and pumps it through the mitral valve and into the left ventricle.
• Left ventricle: The left ventricle pumps the blood through the aortic valve into the aorta and to the rest of the body. 

An electrical signal starts in the sinoatrial node (SA node). First, the atria (two upper chambers) are stimulated and contract for a short period of time. The electrical signal then travels down through the conduction pathways to the heart's ventricles (two lower chambers). This causes them to contract and pump out blood.

The electrical signal then travels from the sinus node to the atrioventricular node (AV node). There, the signals slow down (very briefly) and continue down the conduction pathway through the bundle of His. The bundle of His divides into right and left pathways. These are called bundle branches and they stimulate the right and left ventricles. This completes one heartbeat. A normal heart beats between 60-100 beats per minute.