A look inside your heart
The heart is a four-chambered, hollow organ. The top two chambers are called the right and left atria. The bottom two chambers are called the right and left ventricles. As blood leaves each chamber of the heart, it passes through a valve. The valves make sure blood flows in one direction through the heart.
Blood flow through the heart
With each heartbeat, blood is pumped through your heart to the lungs and body:
- Oxygen-poor blood enters the heart through two large veins into the right atrium and passes through the tricuspid valve into the right ventricle.
- From the right ventricle, blood is pumped through the pulmonic valve into the pulmonary arteries toward the lungs.
In the lungs, blood releases carbon dioxide, a waste product, and picks up oxygen. The pulmonary veins empty oxygen-rich blood, from the lungs, into the left atrium. Blood crosses the mitral valve and enters the left ventricle, which is the main pumping chamber of the heart. From the left ventricle, blood is pumped across the aortic valve into the aorta. The aorta divides into many arteries and provides blood flow to the body.
The coronary arteries
The coronary arteries are the first side-branches of the aorta. They lie on the surface of the heart and supply blood to the heart muscle. The right coronary artery provides blood to the right side of the heart and the bottom of the heart. The left coronary artery originates as the left main trunk, and supplies blood to the front and bottom of the heart by way of the left anterior descending artery, and the side and back of the left ventricle by way of the circumflex artery.
The heart beat
The heart rate is controlled by its own system of nerves which regulate the heart's internal pacemaker, the sinus node. The sinus node rhythmically discharges electrical impulses. These impulses spread through the heart muscle via the heart's electrical system. As the electrical impulses travel into the atria and ventricles, it causes them to contract.