The heart is actually a muscle that works like a pump in distributing blood throughout the body. The heart has four chambers. The two at the top are the left and right atria and the two at the bottom are the left and right ventricles. Blood vessels lead in and out of these chambers.

Oxygenated blood from the lungs flows into your heart and is then pumped out to the rest of your body. Once the blood has delivered the oxygen to the tissues of the body, it returns to your heart and gets pumped back out to the lungs where it will be re-oxygenated.

             structures of the human heart

The human heart has four chambers: two ventricles, each of which is a muscular chamber that squeezes blood out of the heart and into the blood vessels, and two atria, each of which is a muscular chamber that drains and then squeezes blood into the ventricles. The two atria reside at the top of the heart; the two ventricles are at the bottom. And, the heart is divided into left and right halves, so there is a left atrium and left ventricle, as well as a right atrium and right ventricle.

The reason that the heart is divided into halves is because of the two-circuit circulatory system. The right side of the heart can pump blood to the lungs, while the left side of the heart pumps blood to the rest of the body. Blood goes in both directions on each and every pump.

                       The cardiac cycle

Every minute of your life, your heart pumps about 70 times. Every minute of your life, your heart pumps the entire amount of blood that is in the body — 5 liters, which is equivalent to 2-1/2 big bottles of soda. The heart never stops working from the time that it starts to beat when humans are nothing but wee little embryos in their mother’s wombs until the moment they die.

The 8/10th of a second that a heart beats is called the cardiac cycle. During that 0.8-second period, the heart forces blood into the blood vessels plus it takes a quick nap. Here’s what happens in those 0.8 seconds:

  • The left and right atria contract.

  • The left and right ventricles contract.

  • The atria and ventricles rest.

When the atria and ventricles are resting, the muscle fibers within them are not contracting, or squeezing. Therefore, the relaxed atria allow the blood within them to drain into the ventricles beneath them. This period of relaxation in the heart muscle is called diastole.

With most of the blood from the atria now in the ventricles, the atria contract to squeeze any remaining blood down into the ventricles. Then, the ventricles immediately contract to force blood into the blood vessels. This period of contraction in the heart muscle is called systole.

                          Blood pressure

If the terms systole and diastole sound familiar, it is probably because you have heard the terms systolic blood pressure and diastolic blood pressure. In a blood pressure reading, such as the normal value of 120/80 mm Hg, 120 is the systolic blood pressure, or the pressure at which blood is forced from the ventricles into the arteries when the ventricles contract; 80 is the diastolic blood pressure, the pressure in the blood vessels when the muscle fibers are relaxed. The “mm Hg” stands for millimeters of mercury (Hg is the chemical symbol for mercury).

If your blood pressure is 140/90 mm Hg, which is the borderline value between normal and high, that means your heart is working harder to pump blood through your body (140 versus 120), and it is not relaxing as well between pumps (90 versus 80).

A blood pressure reading of 140/90 mm Hg indicates that something is causing your heart to have to work at a much higher level all the time to keep blood flowing through your body, which stresses the heart. The “something” that may be the culprit could be any of the following:

  • A hormonal imbalance

  • A dietary problem, such as too much sodium or caffeine

  • A mechanical problem in the heart

  • A side effect of medication

  • Blockages in the blood vessels

The high pressure in the “pipes” also may lead to damage. Physical damage from high blood pressure is part of a hypothesis of how fibrous plaques are formed in coronary arteries.

               Blood flow through the heart

Your heart muscle is a very efficient pump that delivers blood, oxygen and nutrients to your body.

The heart has four chambers – two on the right and two on the left. Both sides of the heart work together. The right side pumps blood into the lungs and the left side pumps blood into the organs and tissues of your body.

After your blood flows through the body, its life-giving oxygen and nutrients have been depleted. To replenish the oxygen and revitalize the blood, it must pass through the heart and then into the lungs again.

Right side: First the oxygen-depleted blood enters the heart through two large veins, the inferior and superior vena cava and then flows into the right atrium. From the right atrium, it passes through the tricuspid valve and then into the right ventrical. The blood is then pumped through the pulmonary valve and into the lungs.

Once in the lungs, carbon dioxide is removed and oxygen is added to the blood.

Left side: The pulmonary vein empties oxygen-rich blood, from the lungs, into the left atrium. From here, the blood flows from your into your left ventricle through the open mitral valve and finally, it is pumped through the aortic valve into the aorta – the blood vessel that feeds all of the other parts of your body.

When the ventricles are full, the mitral and tricuspid valves close. This prevents blood from flowing backward into the atria while the ventricles contract (squeeze) or “pump.” This pattern is repeated continuously throughout your life, causing blood to flow continuously to the heart, lungs and other parts of the body.

                            Heart beat

The atria and ventricles work together by alternately contracting (squeezing) and relaxing to pump blood through your heart. The heartbeat is triggered by electrical impulses that travel down a special pathway through your heart. The electrical system of your heart is the power source that makes this beating possible.