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The human heart is a fist-sized muscle consisting of four chambers:
the left and right atria, and the left and right ventricles. The right atrium
receives oxygen-depleted blood from the body and delivers it to the right ventricle,
which then pumps the blood to the lungs. The left atrium receives oxygen-rich
blood from the lungs and delivers it to the left ventricle, which then pumps the
blood through the aorta to the rest of the body. Four valves ensure that blood
circulates in the proper direction as it is being pumped.
The heart muscle itself receives oxygen and nourishment from
the coronary arteries, which branch off of the aorta.
Over an average lifetime, the heart beats over 2.5 billion
times. The healthy adult heart pumps about 2,000 gallons of blood each day.
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