How does the heart functions, with respect to the blood flow and heart chambers?

Before we start talking about heart chambers we must see role of heart as a whole in our circulatory system. From the following diagram we get to know that
1. deoxygenated blood from body tissues returns to heart
2. this blood is pumped towards lungs where carbon dioxide is unloaded and oxygen is loaded into blood
3. oxygenated blood from ungs returns to heart
4. this blood is pumped towards body tissues where oxygen is unloaded and carbon dioxide is loaded into blood

The next important point is that heart is divided in right and left parts. Each part has a receiving chamber, Atrium and a dispatching chamber, Ventricle.

Right part of heart receives deoxygenated blood from body tissues and pumps it to lungs while left part of heart receives oxygenated blood from lungs and pumps it to body tissues.

There are AV valves between atrium and ventricle: right AV valve is tricuspid while left AV valve is bicuspid. There are semilunar valves at the base of arteries arising from heart ventricles. Valves help in maintaining a unidirectional blood flow through heart.

Now we will enlist names of blood vessels which are either coming in or going out of heart i.e. veins and arteries associated with it.

I A. Blood enters right atrium through three veins:
1. Superior vena cava
2. Inferior vena cava and
3. Coronary sinus.

Blood from right atrium flows into right ventricle.

I B. Blood leaves right ventricle through the pulmonary artery (which soon divides into left and right branches for respective lungs).

II A. Blood enters left atrium through FOUR pulmonary veins (two from each lung).

Blood from left atrium flows into left ventricle.

II B. Blood leaves left ventricle through ventral aorta.

Now let us revisit the whole story: