How does the heart function?
The heart is a powerful muscle slightly larger than your clenched fist. It works as a pump to send oxygen-rich blood through all parts of your body. Blood contains oxygen and nutrients that every cell in your body needs to survive. The oxygen-rich blood travels throughout the arteries and vessels, nourishing the body so that it can function properly.

Your heart will beat an average of 100,000 times per day. In that time, it pumps more than 4,300 gallons of blood throughout your entire body.

The flow of blood
The heart is divided into two sides. Each side is divided again into two chambers, the atrium (upper chamber) and ventricle (lower chamber). Blood vessels (veins) carry blood to the heart from the rest of the body. This blood carries carbon dioxide and cellular waste products. The blood goes into the right atrium and then to the right ventricle, where it is then pumped to the lungs to dispose of wastes and receive a fresh oxygen supply. From the lungs, the blood returns to the heart. It returns to the left atrium and then to the left ventricle. The blood is then pumped out of the heart by the left ventricle into the aorta. The left ventricle is the chamber of the heart that is responsible for pumping blood to all parts of the body. The aorta sends this blood to small arteries, which carry the oxygen-rich blood to the rest of the body.

Coronary arteries

The right and left coronary arteries branch off the aorta and then divide into smaller branches, supplying all portions of the heart with blood and oxygen. In order for the heart to function properly, it must receive a continuous supply of fresh oxygen-enriched blood. The coronary arteries surround the heart and carry the blood which nourishes the heart muscle. The right coronary artery supplies blood to the right and back sides of the heart. The left coronary artery divides into two main branches–the circumflex and the left anterior descending–supplying blood to the left side of the heart.

Heart valves
There are four heart valves. They are all one-way valves to keep blood moving through the various chambers of the heart.

  1. The mitral valve guards the opening between the atrium and the ventricle in the left side of the heart. It allows blood to flow forward from the atrium to the ventricle, and prevents blood from flowing backwards. The mitral valve has tiny cords attached to the walls of the ventricles. This helps support the valve’s small flaps or leaflets.
  2. The aortic valve, also called a semi-lunar valve, has three segments that prevent the return of the blood from the aorta to the left ventricle. It looks like three half Ping-Pong balls. Valves on the heart’s left side need to withstand much pressure. Sometimes they wear out and leak or become thick and stiff.
  3. The pulmonary valve is located at the junction of the pulmonary artery and the right ventricle. When the right ventricle contracts, the pulmonary valve opens, forcing the blood into the artery which leads to the lungs. It is also a semi-lunar valve. When the chamber relaxes, this valve closes and prevents a backflow of the blood.
  4. The tricuspid valve is located between the upper and lower chamber in the right side of the heart. Its position corresponds to the mitral valve in the left side of the heart.


Early development

At 21 days after conception, the human heart rate begins beating at 75-80 beats per minute and accelerates linearly for the first month of beating.
At 21 days after conception, the human heart rate begins beating at 75-80 beats per minute and accelerates linearly for the first month of beating.

At 21 days after conception, the human heart rate begins beating at 75-80 beats per minute and accelerates linearly for the first month of beating.The human embryonic heart begins beating approximately 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date pregnancy. The human heart begins beating at a rate near the mother’s, about 75-80 beats per minute (bpm). The embryonic heart rate (EHR) then accelerates linearly for the first month of beating, peaking at 165-185 bpm during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 bpm per day, or about 10 bpm every three days, an increase of 100 bpm in the first month.

After peaking at about 9.2 weeks after the LMP, it decelerates to about 150 bpm (+/-25 bpm) during the 15th week after the LMP. After the 15th week the deceleration slows reaching an average rate of about 145 (+/-25 bpm) bpm at term. The regression formula which describes this acceleration before the embryo reaches 25 mm in crown-rump length or 9.2 LMP weeks is:

Age in days = EHR(0.3)+6

There is no difference in male and female heart rates before birth.