How does the heart work?
The human heart has four chambers. The two upper chambers are called the atria. The two lower chambers are called the ventricles. The atria receive blood returning to the heart, and then push it downward to the ventricles. The ventricles, which are larger and stronger, give departing blood a push outward towards its destination.
The heart has two pumps - the right side receives deoxygenated blood from the body and pumps blood to the lungs to pick up oxygen; the much stronger left ventricle takes oxygenated blood coming back from the lungs and circulates it to the rest of the body. Blood flows through the body in an endless figure eight loop.
The right ventricle pumps blood to the lungs so it can get oxygen.
Blood returning from the lungs arrives in the left atrium which pushes it downward to the left ventricle.
The left ventricle pumps blood out to the rest of the body where oxygen will be used by muscles and other tissues to do their work.
Blood returning from various parts of the body arrives in the right atrium. From there it goes to the right ventricle and then to the lungs so it can get more oxygen and the cycle continues.
Blood circulates in two loops as it flows through the heart.
In a healthy, resting adult the heart beats 60 to 100 times per minute. This amounts to 104,000 beats in 24 hours or about 2.5 billion beats in an average lifetime of 70 years.
A normal heart recirculates the 5 to 6 litres of blood in the body every 1.5 minutes. This amounts to over 7,000 litres pumped each day. During strenuous activity, a healthy heart must pump 4 to 7 times its normal output.