The heart – the hardest working muscle in the human body –
even works when you're at rest! Located almost in the center of the
chest, the adult human heart is about the size of a fist. At an average
rate of 80 times a minute, the heart beats about 115,000 times in one
day or about 42 million times in a year.
The cardiovascular system – comprised of the heart and blood vessels
– is responsible for circulating blood throughout your body to supply
the tissues with oxygen and nutrients.
The heart is the muscle that pumps blood filled with oxygen and nutrients
through the blood vessels to the body tissues. The heart is made of:
Four chambers (two atria and two ventricles) that receive blue (deoxygenated)
blood from the body and pump out red (oxygen-rich) blood back to it:
- The atria receive blood coming back to the heart.
- The ventricles pump the blood out of the heart.
- Blood vessels, which include a network of arteries and veins that carry
blood throughout the body: Arteries transport blood from the heart to
the body tissues. Veins carry blood back to the heart.
- Four valves to prevent backward flow of blood: Each valve is designed to
allow the forward flow of blood and prevent backward flow.
- An electrical system that serves as a natural pacemaker and stimulates
contraction of the heart muscle.