The heart is an involuntary^* muscle. Its main job is to pump blood.

The heart pumps blood through its 4 sections called chambers.

The chambers are separated by valves.

An active^* life depends on a healthy heart. Like any other muscle, the heart needs plenty of exercise. Steady aerobic exercise that lasts at least 20 minutes strengthens your heart.

• A healthy heart beats slowly, pushing large amounts of blood on each stroke.
• When you are out of shape, your heart beats faster because it does not move as much blood on each stroke.