We all know that the sound that we hear when we put our head on someone’s chest or the rhythmic vibration that we feel when we put our hand across our chest is caused by the heart pumping blood. But, do you know how that sound was created? Well if not, this is what you are going to find out today after reading this article. First, we will need to take a quick look on the structure of the heart to understand how the sound in the heart is created.

If however, you are knowledgeable about the heart, you have the option of scrolling down and going straight to the heading: "What causes the sound your heart makes?". If not, you should start at: "The structure of the heart". Further down you will also find some interesting facts about the heart under the heading: “Here are some fast Did You Know? facts about the heart”. You should find the additional information interesting.
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The structure of the heart

The heart is a hollow muscular cone-shaped organ, located in the center of the chest (thorax region) between the lungs with its point (apex) directed towards the left. The heart consist of tubes (blood vessels) to receive and eject blood around our body. The arties move (send) blood (oxygenated blood) away from the heart to different parts of our body while, the veins carries blood (deoxygenated blood) from around the body to the heart. It is protected by the ribs and the breastbone which form a sturdy cage around it. The heart is held together in this “cage” by a thick sac called pericardium. a tough layer of muscle, that lies below the heart called diaphragm also protects the heart.

The heart is divided into four chambers: The upper two chambers are the right atrium and left atrium, and the lower two are the right ventricle and left ventricle. There are two chambers on each side with a wall-like divider between them called a septum that separates the left side from the right side of the heart. This wall- like divider separate the oxygenated blood coming from the lung from the deoxygenated blood coming from the body. Oxygenated and deoxygenated blood do not mix in the heart. Blood is pumped through the chambers (the heart), aided by four heart valves (two of each on both side). Two of these valves: The tricuspid valve on the right and the mitral valve on the left regulate blood flow between the atrium and the ventricle on each side. The other two valves: the pulmonary valve on the right allows blood to flow from the right ventricle to the pulmonary arteries, which then supply the lungs. While the aortic valve (on the left) regulates blood flow from the left ventricle to the aorta. Hence, the valves open and close to let the blood flow in only one direction. This means that there are no back flow of blood in the veins or the heart.
What causes the sound your heart makes?
When you listen to your heart using a stethoscope or you listen to someone else heart by placing your head on their chest or by using a stethoscope, you will hear two sounds during each heart beat : a lub-dub lub-dub sound. This sound is created by valves closing on the blood inside the heart. These valves purpose is to prevent blood from flowing backward in any of the four chambers of the heart during the pumping of blood (contraction and relaxation of the heart). The first sound (the lub) happens when the mitral and tricuspid valves close. This happens when the pressure in the ventricles rises above the pressure in the atria, this cause valves to close inorder to prevent back flow of blood from the ventricles into the atria. The next sound (the dub) happens when the aortic and pulmonary valves close after the blood has been squeezed out of the heart. This happens when the left ventricle becomes empty, its pressure falls below the pressure in the aorta, and the aortic valve closes. Like wise, when the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonary valve closes. Thus, during each heart beat you will hear a lub-dub lub-dub sound.

click the heart below to see and hear the heart in motion in a lab.
Diagarm below show the four types of valves in the heart (click on image to enlarge).
Note that each valve has a set of "flaps" (also called cusps). The mitral valve normally has two flaps; the others have three flaps.

The function of the heart
The human heart is a pump made of powerful muscle that circulates blood to and from the body's millions of cells in our body. Every single cell in our body needs oxygen and nutrients to survive. In order for these to reach the cells it is transported throughout the body by the bloodstream.

The circulatory system is similar to a transportation system where the blood acts as a bus and the cells acts as the bus stops. The nutrients, oxygen, and waste product such as carbon dioxide would be the people on the bus and the veins and arteries would be the road that takes them to their destination (the cells). Thus, the blood carries the oxygenated blood (high concentrations of oxygen) along with nutrients to the cells (dropping them off) while at the same time collecting (picking up) the cell’s waste product that is produced by the cell’s activity. This blood will now be deoxygenated blood (high level of carbon dioxide and a very low level of oxygen) since it now drop off and pick up the carbon dioxide produce by the cell activity. It will now return to the lungs where it will pick up oxygen and carry on the cycle (re-circulation of the blood.

How blood moves through the heart - How the heart works


Right side of heart - blood coming from the body (head, trunk, upper and lower limbs)

1a. Blood coming from the body enters the heart through two large veins, the inferior and superior vena cava, emptying deoxygenated blood ( blood with high level of carbon dioxide and low level of oxygen content) into the right atrium.

2a. As the atrium contracts, blood flows from the right atrium into the right ventricle through the open tricuspid valve.

3a.When the ventricle is now full with blood, the tricuspid valve then closes. This prevents blood from flowing backward into the atria while the ventricle contracts.

4a. As the ventricle contracts, blood is then force through the pulmonic valve, leaving the heart and entering into the pulmonary artery which then take the blood to the lungs where it become oxygenated. In other words, the blood releases waste gases (example carbon dioxide) and picks up oxygen thus becoming oxygenated.

Left side of heart - Blood coming from the two lungs

1b.the blood now being oxygenated in the lungs (oxygen -rich blood) returns to the heart through the pulmonary vein which empty this into the left atrium.

2b. As the atrium contracts, blood flows from the left atrium into the left ventricle through the open mitral valve.

3b. When the ventricle is now full with the oxygenated blood, the mitral valve then closes. This prevents blood from flowing backward into the atrium while the ventricle contracts.

4b. As the ventricle contracts, blood is then force through the aortic valve, leaving the heart which then goes into the aorta and to the body.

The cycle repeat itself continuously with out any rest by the heart thus, providing the driving force that is needed to maintain life.

Here are some fast Did You Know? facts about the heart

Your heart beats without your help
Every person's heart beats voluntarily at all times. This means, the heart muscles work on their own without you ever having to consciously commanding it to move or pump blood. This happens whether we are awake (conscious) or a sleep (unconscious). Most other muscles in our body require a direct command from our brain in order for that that muscle to move (respond). For example, you need to make a voluntarily (conscious) decision to move your foot or to hold an object with your hand.

The size of the heart
The average adult heart is about the size of a clenched fist and weighs about 11 ounces.

How fast you heart beat?
The average heart beat is 72 times per minute which is about 100,000 times in one day and about 38 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.

The heart a non stop working machine (organ)
From the very moment your heart starts beating, it never stops until the moment you die. Your heart never rest like other muscles inside the body. It works tirelessly every second. It would surprise you to know that at rest, the heart muscles work twice as hard as the leg muscles of a person sprinting.

The volume of blood pump by the heart
In the normal adult, the heart pumps an average of about five liters of blood per minute, which is then re-circulated continuously through the body. This means the heart pumps 7,200 Liters(1,900 gallons ) per day!

No wonder the heart is something to be treasured and to be taken care of especially, when you steal someone’s heart ! So, don’t go breaking anyone’s heart now :0)