Heart is located between lungs and protected by rib cage. It has a pear shaped structure, wider at the anterior end and narrower at the posterior end. It is covered by two layers of membranes. The membranes are called pericardial membranes. The space between these two layers is filled with pericardial fluid, which protects the heart from shocks.
The heart is divided into four chambers.
1. The upper two chambers are called atria (auricles), and the lower ones are called ventricles.
2. The left atrium and ventricle are smaller when compared to that of right atrium and ventricle. The walls of the ventricles are relatively thicker than atrial walls.
3. Atria receive blood and ventricles send out blood from the heart.