The pulmonary artery carries oxygen–poor blood from the heart to the lungs. In the lungs, carbon dioxide (a waste product) is removed from the blood and exhaled from the body. The blood is then filled with vital oxygen that was inhaled from the air. From the lungs, the blood (now oxygen-rich) travels via the pulmonary veins back to the heart. The blood enters the upper left chamber of the heart (the left atrium) and passes through the mitral valve into the left ventricle. The left ventricle pumps the blood through the aortic valve, out the aorta and to the rest of the body.

Once the body has taken the oxygen from the blood and deposited carbon dioxide into the blood, the blood (now oxygen-poor) returns to the heart. It enters the upper-right chamber of the heart (the right atrium), and passes through the tricuspid valve into the right ventricle of the heart. The right ventricle of the heart then pumps the blood through the pulmonic valve (also known as the pulmonary valve), out the pulmonary artery and to the lungs to get more oxygen.