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How the Heart works: Step by Step Functions with diagrams.

Updated on July 20, 2012

The heart just works, don't try to control it.

Try not to get your heart chained up, it has a cycle to complete.
Try not to get your heart chained up, it has a cycle to complete.

Function of the Heart

Explaining how the heart works can be very confusing if you don't understand the terminology. So, as I explained how the heart works, I will do my best to explain terms that may be foreign to you. If you have questions please feel free to leave them in the comment section below. Electrical properties are one of the main things that allow the heart to work. These electrical properties are responsible for regulating your heart rate and rhythm. The muscles within your heart have automaticity (processing of information in response to stimuli by an organism in a way that is automatic and involuntary, occurring without conscious control), excitability(describes a nerve or tissue that is able to respond to a stimulus), conductivity(ability of an object or substance to transmit electricity), contractility (able to shrink, tighten, narrow same as any muscle), and refractoriness(resistant to control).

How the heart works through the cardiac cycle

The cardiac cycle(sequence of events that occurs when the heart beats) involves a lot of different things, allowing the heart to work. The different phases of the cardiac cycle are described by changes of pressure and volume of the left ventricle during diastole, also known as the filling stage. During diastole(filling stage), both the mitral and tricuspid valves are open. This allows blood to flow in the left and right ventricles respectively. During systole, which is the contraction of the left and right ventricles, both the pulmonic and aortic valves are open to allow blood to flow into the aorta and into the lungs. The blood going to the aorta has oxygen that is ready to go to your organs. The blood on its way to the lungs through the pulmonary artery is going for more oxygen. Two thirds of the cardiac cycle is diastole which is the relaxing and filling of the atria and ventricles. Systole is the contraction and emptying of the atria and ventricles. Learn more about the anatomy of the heart.

Diagram of how the heart works.

How the heart works  AKA Cardiac Cycle
How the heart works AKA Cardiac Cycle

How the heart works

Chemistry and how the heart works

You thought chemistry took two hearts?  Just one actually.
You thought chemistry took two hearts? Just one actually.

The chemistry behind how the heart works

There are a couple terms I would like to define at this moment before I continue. They are myocardial contraction, Sarcoplasmic reticulum, and myofibril sarcomere. A myocardial contraction basically means a contraction of your heart. The same way you would contract your biceps by lifting weights. The Sarcoplasmatic reticulum is where your heart stores calcium. Calcium ions are needed during contractions. Actin is a protein found in muscle, actin works with another protein named myosin. This is where the chemistry portion of the cardiac cycle begins. Calcium ions encourage the actin and myosin proteins to link and overlap one another. These areas that are overlapped are called cross bridges. These protein filaments shorten the sarcomeres causing myocardial contraction or a heartbeat. The heart muscle relaxes when the calcium ions go back into the sarcoplasmic reticulum and then the process starts all over again.

Mechanical properties that determine how the heart works.

Both mechanical and electrical assets work together to determine how well the cardiovascular system in your body works. Cardiac output is the amount of blood pumped from the left ventricle each minute. Blood that is, from the left ventricle is headed out to your body organs and that blood contains oxygen. Cardiac output depends on the relationship between heart rate and stroke volume. So to find what you're cardiac output is you need to take your heart rate times the stroke volume. The cardiac output of an adult is about 4 to 7 L per minute. Cardiac output is not the same for everyone. That is because cardiac output varies according to the size of your body. This is where we get the cardiac index. You can calculate the cardiac index by dividing the cardiac output by the body's surface area. The normal range for this is 2.7 to 3.2 L a minute/m. Heart rate should be something that all of us are familiar with, heart rate is the number of times the ventricles contract each minute. The normal heart rate for an adult is between 60 and 100 beats a minute. Your heart rate is controlled by the autonomic nervous system. Most the time this is how you respond to your environment. While exercising you will see an increase in heart rate. As opposed to sitting your heart rate will decrease. The reason for this is because the oxygen that your body needs increases, so your heart has to be faster to meet the demand. Catecholamines are amino acids found in proteins. The more familiar Catecholamines are epinephrine and norepinephrine, which are responsible for increase heart rate and contractions of the heart. The parasympathetic system slows the heart rate, primarily as a result of the vagus nerve being stimulated. Beta blockers however block this response and decrease heart rate. Stroke volume is the amount of blood the left ventricle can throw out during every contraction. Keeping in mind that the left ventricle is sending the blood with the oxygen back into the system. Stroke volume is affected by many different variables, heart rate, preload, after load, and contractility. Because stroke volume and cardiac output go hand-in-hand, cardiac output is affected by these as well.

Cardiac Output, and how the heart works


Mechanical properties continued

Preload, as I mentioned previously is one of the variables that affects stroke volume. Preload refers to the degree of the muscle fibers being stretched at the end of diastole and just before a contraction. Preload is determined by the amount of blood coming back to the heart from both the vein is system which is the right side of heart in the pulmonary system which is the left side of the heart also known as left ventricular end-diastolic volume. In other words, preload is the amount of blood coming from your internal organs that have used the oxygen. And the amount of blood coming back to the heart from the lungs that has new oxygen and getting ready to leave to go back out your organs again. Both the oxygen poor and the oxygen-rich blood arrived at the heart of the same time, but are headed in different directions. An increase in the volume that the ventricles take in, stretches the heart muscle by length and tension this enhances contraction improves stroke volume. The more the heart is filtering diastole, the more forcefully at contracts. However, excessive volume and pressure in decreased the cardiac output of the heart. After load is the resistance that the ventricles, both left and right must overcome to send blood through the two semi lunar valves known as the aortic and pulmonic valves. This pressure is related to the amount of blood pressure within your arteries and the diameter or size of the blood vessels. Impedance is the preventing of progress, and incoherence is exactly what happens during after load. This is the force the heart must overcome to get that aortic valve to open. The amount of resistance combined with Systemic vascular resistance(blood thickness, size of arteries) is determined of the amount of force or impedance the heart must overcome. A decrease in stroke volume will bring it Inc. recent after load and if the heart is not able to compensate this by itself. There will be a decrease in cardiac output.

Myocardial or muscle contractility is a force of cardiac contraction separate from preload. It affects stroke volume as well as cardiac output. The contractions of the heart can be increased by the sympathetic stimulation, calcium ions being released, and inotropic drugs, such as those prescribed for congestive heart failure. The contraction of the heart is decreased by factors such as, poor oxygen or too much acid in the blood. I hope I have given you a good idea of how the heart works. I understand there may be many questions so feel free to leave comments and questions below. Until next time, take care of your heart.

Best Regards,



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    • profile image

      Hanna orenstein 

      2 years ago

      Yusely 130 / 80 blood pressure is normal - mine is sometime 127/60

      Or 140/56 I have diabetes pls explain to me what does it mean? And I am tired most of the time my age is 73 years old. My diabetes is under control I am taking insulin. I feel like something is wrong with my heart? Tell me if my feeling is correct? hanna

    • profile image


      6 years ago

      the heart is complicated


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