The heart is a hollow muscular organ that pumps blood through the body. It is cone-shaped and weighs about 250 to 300 grams on average. The heart is approximately 12 cm long, 6 cm thick, and 9 cm wide. It has four chambers. The right atrium accepts oxygen-depleted blood from the body and transfers it to the right ventricle, which then propels it to the lungs for oxygenation. After oxygenation in the lungs, the blood travels to the left atrium and is subsequently directed to the left ventricle, from where it is pumped throughout the body. Arteries function as blood vessels that transport blood from the heart to the rest of the body, whereas veins transport blood toward the heart. Both arteries and veins link to capillaries, slender-walled blood vessels that facilitate gas and nutrient exchange between the blood and surrounding tissues. The heart's pumping action maintains a constant supply of oxygen and nutrients throughout the body and carries away the waste.