Heart Chambers

• Figure B shows the inside of your heart and how it’s divided into four chambers. The two upper chambers of your heart are called the atria. They receive and collect blood.
• The two lower chambers of your heart are called ventricles. The ventricles pump blood out of your heart to other parts of your body.

The Septum

• An internal wall of tissue divides the right and left sides of your heart. This wall is called the septum.
• The area of the septum that divides the atria is called the atrial or interatrial septum. The area of the septum that divides the ventricles is called the ventricular or interventricular septum.

Heart Valves

• Figure B shows your heart’s four valves. Shown counterclockwise in the picture, the valves include the aortic (ay-OR-tik) valve, the tricuspid (tri-CUSS-pid) valve, the pulmonary valve, and the mitral (MI-trul) valve.

Blood Flow

• The arrows in figure B show the direction that blood flows through your heart. The light blue arrow shows that blood enters the right atrium of your heart from the superior and inferior vena cavae.
• From the right atrium, blood is pumped into the right ventricle. From the right ventricle, blood is pumped to your lungs through the pulmonary arteries.
• The light red arrow shows oxygen-rich blood coming from your lungs through the pulmonary veins into your heart’s left atrium. From the left atrium, the blood is pumped into the left ventricle. The left ventricle pumps the blood to the rest of your body through the aorta.
• For the heart to work well, your blood must flow in only one direction. Your heart’s valves make this possible. Both of your heart’s ventricles have an “in” (inlet) valve from the atria and an “out” (outlet) valve leading to your arteries.
• Healthy valves open and close in exact coordination with the pumping action of your heart’s atria and ventricles. Each valve has a set of flaps called leaflets or cusps that seal or open the valve. This allows blood to pass through the chambers and into your arteries without backing up or flowing backward.