Introduction to How Heart Disease Works

Heart disease is the leading cause of death in the U.S. At some point in your life, either you or one of your loved ones will be forced to make decisions about some aspect of heart disease. Knowing something about the anatomy and functioning of the heart, in particular how angina and heart attacks work, will enable you to make informed decisions about your health. Heart disease can strike suddenly and require you to make decisions quickly. Being informed prior to an emergency is a valuable asset to you and your family.
In this article we will discuss various heart diseases and how they can lead to a heart attack, or even a stroke. We will also look at how heart attacks are treated and what you should do to prevent heart disease.

The basics Coronary Artery Disease (CAD), Coronary Heart Disease (CHD), Ischemic Heart Disease (IHD) and Arteriosclerotic Cardiovascular Disease (ASCVD) are all different names for the same disease. This disease is caused by atherosclerosis, which is a buildup of fatty deposits (atheroma) in the coronary arteries. See the figure below:Coronary arteries supply blood to the heart muscle. When a blockage occurs in one of these arteries, blood flow to the heart muscle is decreased. This becomes most evident during exertion. During exertion, the heart muscle is working harder and needs more oxygen-enriched blood than usual. By preventing the much needed increase in blood flow, the blockage deprives the heart muscle of oxygen thereby causing the heart muscle to hurt. This chest pain is called angina or Angina Pectoris. When the heart muscle goes without sufficient oxygen, the muscle is said to be ischemic. If cell death occurs it is called infarction. Since a heart attack is cell death of heart muscle (myocardium), it is called a Myocardial Infarction (MI). The condition that causes CAD, angina and heart attacks is called atherosclerosis.
Arteriosclerosis is a more general term for hardening of the arteries. Atherosclerosis is a type of arteriosclerosis that causes a buildup of fatty material (referred to as atheromas and plaques) along the inner lining of arteries. Depending on where these blockages occur, they can cause a number of different outcomes:
If the blockage occurs in a coronary artery, it causes chest pain (angina).
If the blockage is complete, it can cause a heart attack (Myocardial Infarction or MI).
If the blockage occurs in one of the arteries near the brain, a stroke can occur.
If a blockage occurs in a leg artery, it causes Peripheral Vascular Disease (PVD) and can cause pain while walking called intermittent claudication. Atherosclerosis takes many years, even decades to develop and the condition can easily go unnoticed. Sometimes symptoms such as angina will gradually indicate the condition. However, it can also become evident in a sudden and severe way, in the form of a heart attack.
Let's take a look at some of the risk factors for atherosclerosis. Some of these factors are things you can control. By being proactive, you could reduce your risk.

Blood Supply

Coronary arteries are the ones that we try to keep clear by eating a healthy diet. If coronary arteries are blocked a heart attack results.
The heart, just like any other organ, requires blood to supply it with oxygen and other nutrients so that it can do its work. The heart does not extract oxygen and other nutrients from the blood flowing inside it -- it gets its blood from coronary arteries that eventually carry blood within the heart muscle. Approximately 4 percent to 5 percent of the blood output of the heart goes to the coronary arteries (7 ½ ounces/minute or 225 ml/min).
There are two main coronary arteries (figure 6) - The left main coronary artery (1) and the right coronary artery (2) which arise from the aorta. The left main coronary artery divides into the left anterior descending branch (3) and the left circumflex arteries (4). Each artery supplies blood to different parts of the heart muscle and the electrical system.

The heart also has veins that collect oxygen-poor blood from the heart muscle. Most of the major veins of the heart (great cardiac vein, small cardiac vein, middle cardiac vein, posterior vein of the left ventricle, and oblique vein of the left atrium) drain into the coronary sinus which opens into the right atrium.
Coronary artery disease is caused by a blockage in one of the coronary arteries. When a coronary artery is partially blocked, that artery cannot supply enough blood to the heart muscle to meet its needs during exertion. When someone with coronary artery disease exerts himself or herself, it causes chest pain. This is due to lack of blood and oxygen to that part of the heart muscle and is called angina. If the obstruction worsens (more frequent angina episodes, with less exertion) a condition called unstable angina can occur. A heart attack happens when a coronary artery is completely blocked and no blood or oxygen is getting to the heart muscle served by that artery. This also causes chest pain and causes death to the heart muscle served by that artery.

Electrical System

Have you ever wondered what makes your heart beat? How does it do it automatically, every second of every minute of every hour of every day?
The answer lies in a special group of cells that have the ability to generate electrical activity on their own. These cells separate charged particles. Then they spontaneously leak certain charged particles into the cells. This produces electrical impuses in the pacemaker cells which spread over the heart, causing it to contract. These cells do this more than once per second to produce a normal heart beat of 72 beats per minute.
The natural pacemaker of the heart is called the sinoatrial node (SA node). It is located in the right atrium. The heart also contains specialized fibers that conduct the electrical impulse from the pacemaker (SA node) to the rest of the heart (see Figure 4). The electrical impulse leaves the SA node (1) and travels to the right and left atria, causing them to contract together. This takes .04 seconds. There is now a natural delay to allow the atria to contract and the ventricles to fill up with blood. The electrical impulse has now traveled to the atrioventricular node (AV node) (2). The electrical impulse now goes to the Bundle of His (3), then it divides into the right and left bundle branches (4) where it rapidly spreads using Purkinje fibers (5) to the muscles of the right and left ventricle, causing them to contract at the same time.
Any of the electrical tissue in the heart has the ability to be a pacemaker. However, the SA node generates an electric impulse faster than the other tissue so it is normally in control. If the SA node should fail, the other parts of the electrical system can take over, although usually at a slower rate

Although the pacemaker cells create the electrical impulse that causes the heart to beat, other nerves can change the rate at which the pacemaker cells fire and the how strongly the heart contracts. These nerves are part of the autonomic nervous system. The autonomic nervous system has two parts - The sympathetic nervous system and the parasympathetic nervous system. The sympathetic nerves increase the heart rate and increase the force of contraction. The parasympathetic nerves do the opposite.
All this activity produces electrical waves we can measure. The measurement is typically represented as a graph called an electrocardiogram (EKG). Here is an example of three heartbeats from an EKG (Figure 5):

Each part of the tracing has a lettered name:
P wave - coincides with the spread of electrical activity over the atria and the beginning of its contraction.
QRS complex - coincides with the spread of electrical activity over the ventricles and the beginning of its contraction.
T wave - coincides with the recovery phase of the ventricles. Electrical system abnormalities can range from minor premature beats (skipped beats) that do not require treatment, to slow or irregular beats that require an artificial pacemaker

Blood Flow

All blood enters the right side of the heart through two veins: The superior vena cava (SVC) and the inferior vena cava (IVC) (see figure 3).
The SVC collects blood from the upper half of the body. The IVC collects blood from the lower half of the body. Blood leaves the SVC and the IVC and enters the right atrium (RA) (3).
When the RA contracts, the blood goes through the tricuspid valve (4) and into the right ventricle (RV) (5). When the RV contracts, blood is pumped through the pulmonary valve (6), into the pulmonary artery (PA) (7) and into the lungs where it picks up oxygen.Why does it happen this way? Because blood returning from the body is relatively poor in oxygen. It needs to be full of oxygen before being returned to the body. So the right side of the heart pumps blood to the lungs first to pick up oxygen before going to the left side of the heart where it is returned to the body full of oxygen.
Blood now returns to the heart from the lungs by way of the pulmonary veins (8) and goes into the left atrium (LA) (9). When the LA contracts, blood travels through the mitral valve (10) and into the left ventricle (LV) (11). The LV is a very important chamber that pumps blood through the aortic valve (12) and into the aorta (13). The aorta is the main artery of the body. It receives all the blood that the heart has pumped out and distributes it to the rest of the body. The LV has a thicker muscle than any other heart chamber because it must pump blood to the rest of the body against much higher pressure in the general circulation (blood pressure).
Here is a recap of what we just discussed. Blood from the body flows:
to the superior and inferior vena cava,
then to the right atrium
through the tricuspid valve
to the right ventricle
through the pulmonic valve
to the pulmonary artery
to the lungs

2.Chambers and Valves

The heart is divided into four chambers: (see Figure 2)
1.right atrium (RA)
2.right ventricle (RV)
3.left atrium (LA)
4.left ventricle (LV)

Each chamber has a sort of one-way valve at its exit that prevents blood from flowing backwards. When each chamber contracts, the valve at its exit opens. When it is finished contracting, the valve closes so that blood does not flow backwards.
The tricuspid valve is at the exit of the right atrium.
The pulmonary valve is at the exit of the right ventricle.
The mitral valve is at the exit of the left atrium.
The aortic valve is at the exit of the left ventricle.
When the heart muscle contracts or beats (called systole), it pumps blood out of the heart. The heart contracts in two stages. In the first stage, the right and left atria contract at the same time, pumping blood to the right and left ventricles. Then the ventricles contract together to propel blood out of the heart. Then the heart muscle relaxes (called diastole) before the next heartbeat. This allows blood to fill up the heart again.
The right and left sides of the heart have separate functions. The right side of the heart collects oxygen-poor blood from the body and pumps it to the lungs where it picks up oxygen and releases carbon dioxide. The left side of the heart then collects oxygen-rich blood from the lungs and pumps it to the body so that the cells throughout your body have the oxygen they need to function properly.
Pulse Rates
Everyone's pulse (average heart rate per minute) changes as we age. Here is a chart of average pulse rates at different ages:

Age Pulse
Newborn 130

3 months 140

6 months 130

1 year 120

2 years 115

3 years 100

4 years 100

6 years 100

8 years 90

12 years 85

adult 60 - 100

How Your Heart Works

Inside This Article
1.
Introduction to How Your Heart Works
Chambers and Valves
3.
Blood Flow
4.
Electrical System
5.
Blood Supply
6.
Lots More Information
7.
See all The Body articles
Everyone knows that the heart is a vital organ. We cannot live without our heart. However, when you get right down to it, the heart is just a pump. A complex and important one, yes, but still just a pump. As with all other pumps it can become clogged, break down and need repair. This is why it is critical that we know how the heart works. With a little knowledge about your heart and what is good or bad for it, you can significantly reduce your risk for heart disease.
Heart disease is the leading cause of death in the United States. Almost 2,000 Americans die of heart disease each day. That is one death every 44 seconds. The good news is that the death rate from heart disease has been steadily decreasing. Unfortunately, heart disease still causes sudden death and many people die before even reaching the hospital.
The heart holds a special place in our collective psyche as well. Of course the heart is synonymous with love. It has many other associations, too. Here are just a few examples:
have a heart - be merciful
change of heart - change your mind
to know something by heart - memorize something
broken heart - to lose love
heartfelt - deeply felt
have your heart in the right place - to be kind
cry your heart out - to grieve
heavy heart - sadness
have your heart set on - to want something badly Certainly no other bodily organ elicits this kind of response. When was the last time you had a heavy pancreas?
In this article, we will look at this important organ so that you can understand exactly what makes your heart tick.
The heart is a hollow, cone-shaped muscle located between the lungs and behind the sternum (breastbone). Two-thirds of the heart is located to the left of the midline of the body and 1/3 is to the right (see Figure 1).
Figure 1[Please note - Medical illustrations assume that the patient isfacing you so that the right and left correspond to the patient's right and left. That's why the left and right labels here seem backwards.]
The apex (pointed end) points down and to the left. It is 5 inches (12 cm) long, 3.5 inches (8-9 cm) wide and 2.5 inches (6 cm) from front to back, and is roughly the size of your fist. The average weight of a female human heart is 9 ounces and a male's heart is 10.5 ounces. The heart comprises less than 0.5 percent of the total body weight.
The heart has three layers. The smooth, inside lining of the heart is called the endocardium. The middle layer of heart muscle is called the myocardium. It is surrounded by a fluid filled sac call the pericardium.
Heart SoundsWhen someone listens to your heart with a stethoscope the sound is often described as lub-dub lub-dub. The first heart sound (lub) is caused by the acceleration and deceleration of blood and a vibration of the heart at the time of the closure of the tricuspid and mitral valves. The second heart sound (dub) is caused by the same acceleration and deceleration of blood and vibrations at the time of closure of the pulmonic and aortic valves.

Philosophy of Mahatma Gandhi in His Own Words

I know the path. It is straight and narrow. It is like the edge of a sword. I rejoice to walk on it. I weep when I slip. God's word is: 'He who strives never perishes.' I have implicit faith in that promise. Though, therefore, from my weakness I fail a thousand times, I will not lose faith, but hope that I shall see the Light when the flesh has been brought under perfect subjection, as some day it must.

Search for Truth : I am but a seeker after Truth. I claim to have found a way to it. I claim to be making a ceaseless effort to find it. But I admit that I have not yet found it. To find Truth completely is to realize oneself and one's destiny, i.e., to become perfect. I am painfully conscious of my imperfections, and therein lies all the strength I posses, because it is a rare thing for a man to know his own limitations.
Trust in God : I am in the world feeling my way to light 'amid the encircling gloom'. I often err and miscalculate… My trust is solely in God. And I trust men only because I trust God. If I had no God to rely upon, I should be like Timon, a hater of my species.No Secrecy :I have no secret methods. I know no diplomacy save that of truth. I have no weapon but non-violence. I may be unconsciously led astray for a while, but not for all time. My life has been an open book. I have no secrets and I encourage no secrets.

Guidance :I claim to have no infallible guidance or inspiration. So far as my experience goes, the claim to infallibility on the part of a human being would be untenable, seeing that inspiration too can come only to one who is free from the action of opposites, and it will be difficult to judge on a given occasion whether the claim to freedom from pairs of opposites is justified. The claim to infallibility would thus always be a most dangerous claim to make. This, however, does not leave us without any guidance whatsoever. The sum-total of the experience of the world is available to us and would be for all time to come.
Self-sacrifice and Ahimsa : I am asking my countrymen in India to follow no other gospel than the gospel of self-sacrifice which precedes every battle. Whether you belong to the school of violence or non-violence, you will still have to go through the fire of sacrifice and of discipline.

No Defeatism : Defeat cannot dishearten me. It can only chasten me . . . . I know that God will guide me. Truth is superior to man's wisdom.

Trust : It is true that I have often been let down. Many have deceived me and many have been found wanting. But I do not repent of my association with them. For I know how to non-co-operate, as I know how to co-operate. The most practical, the most dignified way of going on in the world is to take people at their word, when you have no positive reason to the contrary.

My Leadership and Non Violence : They say I claim to understand human nature as no one else does. I believe I am certainly right, but if I do not believe in my rightness and my methods, I would be unfit to be at the helm of affairs.

My Work : I am content with the doing of the task in front of me. I do not worry about the why and wherefore of things… Reason helps us to see that we should not dabble in things we cannot fathom.