Structure of Human Heart
The human heart is a vital organ that functions as the center of the circulatory system. It is a muscular organ roughly the size of a fist, located slightly left of the center of the chest. The heart is divided into four chambers: the left and right atria (upper chambers) and the left and right ventricles (lower chambers).

Key Components of the Heart
- The Atria: The atria receive blood from the body and lungs, acting as holding chambers before pumping it into the ventricles.
- The Ventricles: The ventricles are responsible for pumping blood out of the heart to the body and lungs.
- Valves: The heart contains four valves that ensure blood flows in the correct direction and prevents backflow. These valves are the tricuspid valve, pulmonary valve, mitral valve, and aortic valve.
- Blood Vessels: The heart is connected to a network of blood vessels that deliver oxygenated blood to the body and return deoxygenated blood back to the heart.

Function of the Heart
The heart's main function is to pump blood throughout the body, delivering oxygen and nutrients to cells while removing waste products. It achieves this through a rhythmic contraction and relaxation process known as the cardiac cycle.

Circulation of Blood
- Deoxygenated blood enters the right atrium from the body through the superior and inferior vena cava.
- The blood moves to the right ventricle and is pumped to the lungs through the pulmonary artery for oxygenation.
- Oxygenated blood returns to the heart via the pulmonary veins, enters the left atrium, and flows into the left ventricle.
- The left ventricle pumps oxygenated blood to the rest of the body through the aorta.
In conclusion, understanding the structure and function of the human heart is crucial for comprehending how blood circulates through the body to sustain life.