The human heart is a muscular, cone-shaped organ about the size of a fist, weighing 250–350 grams. It has a reddish-brown color with a smooth outer surface covered by the pericardium. The heart consists of four chambers—two smaller, thin-walled atria on top and two larger, thick-walled ventricles below. Major arteries and veins, including the aorta and vena cava, extend from it. Inside, valves separate chambers, ensuring one-way blood flow. The left ventricle is the most muscular