Once the heart stops beating, it no longer pumps blood and oxygen. Cells begin to die, and the body cools and stiffens. Decomposition begins, and the rate of decomposition depends on the conditions surrounding the body.
Blood Pools
Gravity causes blood to gradually drain from the blood vessels of upper areas into the vessels of the body located closest to the ground.
Changes in Color
The skin of the upper areas pale gradually as they lose blood. As it collects in the lower areas, those areas darken.
Cooling
Typically, it takes about 12 hours for the deceased body to feel cool to the touch and 24 hours for the body to cool completely. Surrounding temperature will affect actual cooling time.
Rigor Mortis
Rigor mortis--which is the gradual stiffening of the body after death--begins after three hours and lasts for 36 hours. This is associated with the buildup of lactic acid in the body.
Decomposition
As the cells die, enzymatic and bacterial activity begin the process of decomposition. Gases swell the body. The flesh and tissues begin to liquefy, and this continues until the body dries out.
