Hour 1
At the moment of death, all of the muscles in the body relax, a state called
primary flaccidity. Eyelids lose their tension, the
pupils dilate, the jaw might fall open, and the body's joints and limbs are flexible. With the loss of tension in the muscles, the skin will sag, which can cause prominent joints and bones in the body, such as the jaw or hips, to become pronounced.
The
human heart beats more than 2.5 billion times during the average human lifespan, circulating about 5.6 liters (6 quarts) of blood through the circulatory system. Within minutes of the heart-stopping, a process called
pallor mortis causes the usually pinkish tone of a Caucasian person to grow pale as blood drains from the smaller veins in the skin.
Hours 2 to 6
Because the heart no longer pumps blood, gravity begins to pull it to the areas of the body closest to the ground (pooling), a process called
livor mortis. If the body remains undisturbed long enough (several hours), the parts of the body nearest the ground can develop a reddish-purple discoloration (resembling a bruise) from the accumulating blood. Embalmers sometimes refer to this as the "postmortem stain."
Beginning approximately in the third hour after death, again depending upon numerous factors, chemical changes within the body's cells cause all of the muscles to begin stiffening. Known as
rigor mortis, the first muscles affected include the eyelids, jaw, and neck. Over the next several hours, rigor mortis spreads up into the face and down through the chest, abdomen, arms, and legs until it reaches the fingers and toes.
The Physical Changes After Death
(Both sections from the article have been snipped by me for focus.)