The heart is a muscular organ located in the chest, slightly to the left of the centre. It plays a critical role in the circulatory system, pumping blood throughout the body to deliver oxygen and nutrients to various tissues and organs while removing waste products. The heart is essential for sustaining life. 

The human heart is roughly the size of a closed fist and is located in the chest, slightly to the left of the midline. It is enclosed by a protective sac called the pericardium. The heart is divided into four chambers: two atria (the left and right atrium) and two ventricles (the left and right ventricle). 

The primary function of the heart is to pump blood throughout the body. It accomplishes this through a rhythmic and coordinated contraction-relaxation cycle. The right side of the heart receives oxygen-poor blood from the body and pumps it to the lungs for oxygenation. The left side of the heart receives oxygen-rich blood from the lungs and pumps it to the rest of the body.