Valves

• The heart has four main valves: the tricuspid valve, the mitral valve, the pulmonary valve and the aortic valve. These valves separate the various chambers of the heart. As they contract, they allow blood to enter a chamber and prevent it from re-entering the previous chamber.
  
  

Veins and Arteries

• The main vein in the heart is the pulmonary vein. It is responsible for carrying oxygen-filled blood from the lungs into the left atrium. The main artery in the heart, the pulmonary artery, transports de-oxygenated blood from the right ventricle into the lungs. A series of blood vessels known as the coronary arteries carry oxygen and nutrient-rich blood to the cardiac muscle tissue itself.
  
  

Ventricles

• As the right atrium contracts, the right ventricle receives de-oxygenated blood. From here, blood flows into the pulmonary artery into the lungs. The left ventricle receives blood as the left atrium contracts. As the aortic valve opens, blood from the left ventricle flows throughout the body.
  
  

Atrium

• There are two atrium chambers in the heart. The right atrium receives de-oxygenated blood from the body and from here, the blood is pumped into the right ventricle. The left atrium receives oxygenated blood from the lungs and from here, the blood is pumped into the left ventricle.
  
  

Vena Cava

• There are two veins that bring de-oxygenated blood from the body into the heart. The superior vena cava brings de-oxygenated blood from the head into the heart while the inferior vena cava brings blood from the legs and lower torso.
  
  

Aorta

• The aorta is the largest blood vessel in the body and is approximately the width of your thumb. The aorta transports blood from the left ventricle throughout the rest of the body.