This oxygen-poor blood then passes through the tricuspid valve into the right ventricle. The tricuspid valve closes after the blood passes through to prevent it from flowing back into the right atrium.The two largest veins in the body, the superior and inferior vena cava, bring the oxygen-poor (blue) blood to the heart into the right atrium.The four chambers of the heart are attached to major veins or arteries that either bring blood into or carry blood away from the heart. How blood circulates through the heart and body The aortic valve is located between the left ventricle and the aorta.The mitral valve is between the left atrium and the left ventricle.

The pulmonary valve is between the right ventricle and the pulmonary artery.The tricuspid valve is between the right atrium and the right ventricle.

There are four valves within the heart. Each valve has flaps that prevent blood from flowing in the wrong direction - opening to allow forward flow of blood and closing to prevent backward flow.

Muscular walls, called septa or septum, divide the heart into two sides and keep the two kinds of blood from mixing.

On the left side of the heart, the left atrium and left ventricle combine to pump oxygenated blood back through the body.

On the right side of the heart, the right atrium and right ventricle work to pump oxygen-poor blood returning from the body back to the lungs to be reoxygenated.

The heart is a two-sided pump made up of four chambers: the upper two chambers called atria and the lower two called the ventricles. View this video with a transcript The structure of the heart

Normal heartbeat for child