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Internal anatomy of the human Heart (Explanation of four heart chambers)

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There are four heart chambers,they are
  1. Right atrium
  2. Right ventricle 
  3. Left atrium 
  4. Left ventricle
Each of these chambers plays a role in the continuous process of blood circulation.Valves between these chambers permit the passage of blood in one direction and prevent its backflow.
Right Atrium
Right atrium receives venous blood from mainly two source
  • The systemic circuit
  • From the heart muscle itself.
Three major veins empty into the right atrium:
Superior vena cava (SVC) drains venous  blood from the head, upper limbs, and superior regions of the trunk.
Inferior vena cava (IVC) drains blood from the lower limbs and trunk.
Coronary sinus drains blood from the heart wall.
The interatrial  septum forms a wall between the right and left atria.

Right Atrioventricular (AV) Valve
These valve separates the right atrium from the right ventricle.It is also called as tricuspid valve,and it has three triangular flaps.Venous blood flows from the right atrium pass through the valve into the right ventricle. When the right ventricle begins to contract tricuspid valve closes and it prevent bloodbackflow into the right atrium.

Right Ventricle
Right Ventricle receives deoxygenated venous blood from the right atrium.The right and left ventricles are separated by  an interventricular septum .
Papillary muscles are present  on the internal wall surface,thsese are cone-shaped, muscular projections and anchor chordae tendineae ,they are attached  to the cusp of the right atrioventricular valve and prevent  everting and flipping of valve into the right atrium when contracting.

Pulmonary Trunk
At its superior end pulmonary trunk narrows into a smooth-walled, conical region called the conus arteriosus. The pulmonary semilunar valve is situated at junction between the end of the right ventricle and the entrance into the pulmonary trunk.Pulmonary trunk divides into right and left pulmonary arteries it carry deoxygenated blood to the lungs.

Semilunar Valves
Located within the walls of both ventricles,seen immediately before the connection of the ventricle to the pulmonary trunk and aorta.The semilunar valve is composed of three thin, pocketlike semilunar cusps.When blood is pumped into the arterial trunks, it pushes against the cusps and forces the valves open. This valve prevent backward flow of blood into the ventricles,when ventricular contraction ceases.

Left Atrium
Left atrium recieves the oxygenated blood from the pulmonary veins to the left atrium. 
The smooth posterior wall of the left atrium has openings for approximately four pulmonary veins.
Two left pulmonary veins.
Two right pulmonary veins.

Left Atrioventricular (AV) Valve
Thses valve separates the left atrium from the left ventricle. This is called as bicuspid valve or the mitral valve. Left AV valve has chordae tendineae similar to that present in right AV valve.Oxygenated blood flows from the left atrium into the left ventricle. When the left ventricle begins to contract the AV valve Is forced closed .They  prevents blood backflow into the left atrium.

Left Ventricle
Left ventricle is largest of the four heart chambers.Its wall is three times thicker than the right ventricular wall.The main purpose of thick walls is to generate enough pressure to force the oxygenated blood from the lungs into the aorta and then through the entire systemic circuit.The right ventricle only has to pump blood to the nearby lungs. Trabeculae carneae in the left ventricle are more prominent.There are two large papillary muscles which attach to the chordae tendineae that help to support the left AV valve. The aortic semilunar valve is situated at the junction between the end of the left ventricle and the entrance into the aorta.