Everything You Need To Know About the Heart


The human body is composed of approximately 37.2 trillion cells, all of which require raw materials to survive and maintain their function. Oxygen, energy nutrients, and a variety of other environmental inputs must be collected and transported around the body for the cells to consume. [1] 

To accomplish this feat, the circulatory system must pass approximately 7000 liters of blood through the body each day. With constant changes in environment, fluid balance, and body position, this can become challenging.  

The circulatory system is comprised of a vascular network coupled with a muscular pump called the heart. Rhythmic beating of the heart ejects blood through a pressurized system which allows for maximum movement and supply delivery to the various cellular tissues in the body.  

Surprisingly, the heart only accounts for 7 percent of total energy expenditure per day, which is less than the brain, liver, and kidneys respectively. However, the heart remains under constant tension and rapidly shifting conditions, which can quickly wear the system down and lead to disease. 

The grim reality is that cardiovascular disease (CVD) is the number one cause of death, not only in the United States, but worldwide. CVD accounts for approximately 800,000 deaths annually in the United States, with most of the cases being attributed to coronary heart disease (CHD). The other cases are due to heart failure. [2] 

More frightening, the incidence and cost of CVD continues to rise. Not just the cost of CVD treatment, but the amount spent on research—which was estimated to be about 3 billion dollars in 2008, almost a decade ago—is rising as well. [3] 

Many factors in our environment contribute to the increased risk of heart disease. Poor diet, lack of exercise, constant stress, and exposure to environmental toxins are all culpable. To avoid CVD requires an understanding of the system and how it can be negatively affected by everyday situations. Let’s start with some fun facts about the heart: 

6 Interesting Facts About the Heart 

  1. The average heartbeat occurs about 60-100 times per minute which extrapolates out to approximately 100,000 beats per day. [4] 
  2. The total distance of all the blood vessels in the human body is over 60,000 miles long. [4] 
  3. The heart can generate enough energy to drive a truck 20 miles in a single day. [5] 
  4. Blood ejects from the heart at about 1 mile per hour and returns at about 43 inches per hour. [5] 
  5. Women typically have faster heartbeats than men. [5] 
  6. The heart can generate enough pressure to squirt blood thirty feet. [5] 

Heart Anatomy 

The heart is a self-stimulating pump that drives blood through a network of vessels throughout the body. The blood vessels are separated into three categories: arteries, veins, and capillaries.  


The vessels which carry blood away from the heart. Arteries are most associated with oxygenated blood; however, this would not be entirely correct because the pulmonary artery carries deoxygenated blood away from the heart to the lungs for gas exchange.  

The structure of an artery is essentially a round tube with a narrow center, with two layers of tissue and a thick middle layer composed of muscle forming the tube walls. The musculature of an artery is there to combat high pressure and to maintain elasticity for changing conditions. [6] 


Veins are the opposite of arteries; they carry blood back toward the heart. They have a similar construction to that of arteries, except that the middle layer is much less thick and muscular. Veins do not exist under the same amount of pressure that arteries are. They are flat, with a much greater inner space. Veins in body spaces below the heart contain valves to prevent back flow and blood pooling. [6] 


Capillaries are the junction between arteries and veins. Arteries empty into capillary beds which supply the surrounding tissue with materials in a process called perfusion. Capillaries are smaller and often porous to allow for the exchange of gases and nutrients/waste products. There are a variety of capillary types, found in different regions of the body. [6] 

Where is the Heart Located?

The heart is found in the chest, positioned behind the sternum. It is a little bigger than a human fist and is mostly muscle. Because of it’s proximity to the lungs, the heart is surrounded by a cavity called the pericardium 

The heart has four chambers which coincide with the right and left halves of the heart. The two upper chambers are called the atria (plural of atrium) and the bottom chambers are called the ventricles. The atria are smaller and are much less muscular than the ventricles. The ventricles can be differentiated by which side of the heart they are found. The left side is thicker and more muscular than the right. [7] 

The right atria and ventricle are connected by a valve, as are the left atria and ventricle. The valves are designed to allow for pressure-regulated openings and closings. The valve on the right is called the tricuspid valve, while the valve on the left is most commonly called the mitral valve. The valves’ design is specific, to prevent blood back flow when movement occurs through the chambers.  

There are four large blood vessels connecting directly to the heart. The vena cava is the largest vein in the body,  and it empties into the right atrium. The aorta is the largest artery, and it receives oxygenated blood ejected by the left ventricle. The other two blood vessels are the pulmonary artery and vein, which shuttle blood to and from the lungs for gas exchange. [7] 

The heart requires a highly coordinated contraction pattern to efficiently drive blood flow through the body. Precise rhythm that can also be adapted for rapid change in physiological state and complete contraction are two important features of the heart.  

To accomplish this coordinated response, the heart has a specialized conductivity system that begins with a patch of excitable cells called the sinoatrial (SA) node. The SA node is found in the right atrium and is the pacemaker of the heart. The electrical-based pulse the heart uses to contract begins in the SA node. 

The SA node transfers the signal to the atrioventricular (AV) node. The AV node is also found in the right atrium and connects the rest of the conductive system to the rest of the heart. The AV node gives way to right and left branches, which spread to the many cells of the heart through Purkinje (poor-KIN-jee) fibers. [7] 

Heart Function 

The heart’s primary function is to pump blood throughout the body. Deoxygenated blood is received by the right side of the heart and oxygenated blood is ejected by the left. This task is made difficult because of the overall resistance of the system and the effects of gravity.  

The basic premise is simple: blood moves through the system, providing transport of a variety of vital materials. Blood also collects wastes for disposal, and must be continually circulated to maintain balance.  

The heart receives deoxygenated blood from the system and sends it to the lungs for gas exchange. Blood returns to the heart, saturated with oxygen from the lungs, and is then pumped to the rest of the body.  

The right side of the heart receives blood from the vena cava, which empties into the right atrium. Blood flows from the right atrium into the right ventricle, which pumps the blood through the pulmonary artery to the lungs. Blood then returns to the heart through the pulmonary vein to the left atrium. After blood empties into the left ventricle, it is ejected to the entire body and the cycle begins again.  

The function of the heart is not complex, but it is vital. What makes the heart susceptible are the conditions under which it must operate. Two factors are important for the heart to function properly: a pressurized system and self-stimulatory ability. 

The first is related to regulated pressure throughout the system. The ejection of blood from the heart is impeded by peripheral resistance, which is the decreasing size of the blood vessel. But if any blood vessel along the path were collapsed, it would create an even greater amount of resistance and blood flow would not reach the required distance.  

Therefore, the body works with a decreasing pressure ratio, from the ejection point to the return point of blood. The highest pressure is found in the left ventricle and the lowest pressure is found in the vena cava. [8] 

This allows the ejection of blood to spread to the capillary beds. As it moves through the system, it is effected by steadily decreasing resistance. The pressure, however, must also be regulated. Too high can cause undue strain on the heart; too low leads to fatigue and syncope (fainting).  

The second factor is the ability to self-stimulate. A variety of cells in the body can generate electrical pulses. Nerves and muscle cells are the most prominent; however, there is usually a stimulatory response that generates what is called an action potential.  

Action potentials are a wave-like movement of ionic nutrients that create an electrical pulse and are very important for human physiology. Th SA node found in the right atrium of the heart is an example of a self-stimulatory cell type which can generate a repeated action potential. [9] 

The firing of the SA node spreads to the AV node and then spreads to the entire heart, to coordinate contraction at a specific rate. This allows for the two-thump heartbeat that we have grown to understand. The contraction wave spreads down the atria to the ventricles so that they fire in sequence. 

The difficulty of this process is that the SA node has a single fire rate, which is approximately 100 beats per minute. To slow and speed this rate up in response to environmental change, the SA node is regulated by the autonomic nervous system.  

Heart Disease 

Heart disease can be many things, but ultimately heart disease comes down to two primary factors: 

  • Loss of oxygen to the heart muscle itself.  
  • High peripheral resistance, leading to over stress of the heart.  

There are congenital heart diseases, which occur at birth. These diseases are the most common birth defects and affect primarily children. There are a variety and most can be easily corrected when diagnosed. [10] 

However, the great killer of a generation—cardiovascular disease—is most expressed in adults. The two primary diseases of the heart are acute myocardial infarction (AMI) and congestive heart failure. [11] 

Heart attacks are the more common name for an acute myocardial infarction. This type of heart disease is developed, over time, by a clogged coronary artery. The clog is created by an atherosclerotic clot forming in the arteries which supply the heart muscle with blood. 

The result is lack of oxygen to very oxygen-dependent muscle. The cells start to die, which can lead to death. There are a variety of symptoms related to a heart attack, which include angina pectoralis (chest pain) and shortness of breath.  

The other common form of heart disease is congestive heart failure, which is due to poor blood ejection. In this case, the heart has becomes weakened over time due to left ventricular hypertrophy. This means that the left ventricle has become stretched and enlarged, which weakens ejection forces.  

Atherosclerosis is one of the primary causes of high blood pressure. The increased pressure in the system places added stress to the heart muscle, especially the left ventricle. This begins to expand the chamber and weaken the ability to pump blood.  

There are other causes of high blood pressure, but atherosclerosis is the most common issue that is related to most heart disease. Atherosclerosis is a progressive hardening of the arteries due to inflammation in the blood vessels. [12] 

Heart Health 

Google “heart health” and you will get 42 million hits. Heart health has been one of the most researched topics, and one of the most hotly debated. Since the 1940s, heart disease has been studied due to the rising death toll. The first major study to gain recognition was the 1948 Framingham heart study. 

A town in Massachusetts became the site for an epidemiological study on the association between diet and heart disease. The Framingham study was concerned with cholesterol levels in the blood. It was discovered that men with high LDL cholesterol were at greater risk of atherosclerosis. [13] [14] 

It was determined that diets high in cholesterol and saturated fat were associated with increased risk of heart disease. This philosophy became the diet revolution of several generations. Low-fat and even no-fat became the calling card for a variety of organizations, including the American Heart Association (AHA). 

High carbohydrates/low fats would be the prevailing thought for decades and in many ways, is still considered the best defense against heart disease. However, not all agree with this thought. Cardiologists such as Dr. Robert Atkins believed that high fat/low carbohydrate diets were a better option. [15] 

So, what exactly does heart health mean then? The low saturated fat diet that has been preached for decades is now being questioned, and sugar consumption has been shown to have a stronger link to progression of heart disease. [16] [17] 

The dynamics of heart disease actually begins in the liver. It has been well established that non-alcoholic fatty liver disease, which is caused by excessive sugar intake, is greatly linked to heart disease [18] 

LDL cholesterol has long been linked to heart disease, and is the major risk factor for development of atherosclerosis. LDL particles get stuck between the cells lining the inside of an artery and are then destroyed by a combination of reactive oxygen species (free radical) and the immune system. 

This process is what causes clots to be formed. This has been well established; however, what has not been discussed in community health is LDL particle size. There is a range in LDL particle size, consisting of larger, less dense varieties and smaller, more dense ones. [19] 

The smaller varieties are associated with greater risk of heart disease and are less associated with high-fat diets. Yes, eating fats will raise LDL cholesterol; however, it raises both HDL (good) cholesterol and the larger, less dense LDL particle.  

A heart-healthy diet begins with fresh vegetables and fruits. Vitamins C and E are considered anti-oxidant which can reduce the stress of free radicals. Other non-nutritive chemicals, such as phytochemicals, can play a role as antioxidants as well. 

Low-carbohydrate diets have proven to be effective, especially when the amount of free sugar is reduced. Also drink plenty of water and reduce caffeine intake if you are susceptible to anxiety, to avoid raising blood pressure. 

Exercise of all types is encouraged as well. Physical activity clears fat and sugar from the blood and positively modifies the heart and blood vessels.  

The Takeaway

The heart is a vital piece of the health puzzle. A healthy diet rich in whole foods, coupled with exercise, can greatly reduce the risk of heart disease, even in those with family history.

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William Fredericks is an exercise physiologist located in Florida. Bill has been practicing for 15+ years and has accumulated a wealth of knowledge and experience in that time. Bill has also served as a college professor at both Florida State University and Tallahassee Community College. Bill has taught anatomy and physiology lab, exercise physiology, sports nutrition, and nutrition, which he still currently teaches. Bill has a bachelor in exercise physiology and a masters in nutrition science. Bills education lead him in the direction of a variety of topics which includes biology, chemistry, and biomedical science. Bill possesses a deep understanding about health and the human body which he uses to educate others on how to make improvements


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