Your heart is the most important muscle in your body. Its role in transporting oxygenated blood to your body's tissues and helping remove waste products from the bloodstream. The heart is a hallow muscular organ that is roughly the size of a man's fist, averaging approximately 5 inches in length, 3.5 inches in width and 2.5 inches in thickness. It weighs about 10.5 ounces in the male and 8.75 ounces in the female.