Your heart is a fist-sized muscle, which is divided into four chambers. Each chamber is like a separate room, with one-way doors (valves) that let blood in and out.
The two upper chambers in your heart are called the atria. Blood comes into the atria from the body or lungs.
The two lower chambers in your heart are called ventricles. They are the pumping chambers of your heart. The ventricles are very strong because they have to pump hard enough to push blood through your lungs and entire body.
The heart has its own electrical system which causes it to beat. It's made up of three parts:
- Sinus Node (also S-A or sinoatrial node): the heart's internal pacemaker which controls the rate and rhythm of your heartbeat.
- AV node (atrioventricular node): makes the electrical connection between the atria and ventricles
- His-Purkinje system: carries the electrical signals throughout the ventricles to make them contract
With each heartbeat, an electrical signal travels from the top of your heart to the bottom, causing your heart to contract and pump blood. The process repeats with each new heartbeat.
The right and left sides of the heart have different jobs. Oxygen-poor blood from the body enters the right atrium and passes through the Tricuspid valve into the right ventricle. The blood is pumped out of the right ventricle, passing through the Pulmonary valve, into the lungs where it picks up oxygen. The oxygen-rich blood re-enters the heart into the left atrium. It passes through the Mitral valve into the left ventricle. The blood exits the heart, passing through the Aortic valve and into the Aorta. The left ventricle is the largest and strongest chamber because it has to pump blood to the entire body so that the cells throughout your body have the oxygen needed to function properly.