A 15-minute primer on the heart and how it words

The heart chambers and heart valves
The heart is the body's pump. This article shows how it all works.

The coronary arteries
This article describes the coronary arteries, the vital blood vessels that supply the energy-hungry heart muscle.

The cardiac electrical system
The heart's electrical system coordinates the beating of the heart, and is critical to making sure the system works the way it's supposed to.

The Heart's Chambers and Valves

The purpose of the heart is to pump the blood that bathes every organ of the body. The blood carries oxygen and nutrients to the tissues, and removes waste products from the tissues. If the pumping action of the heart is disrupted, the body’s organs begin to fail very quickly.Therefore, life itself is dependent on the efficient operation of the heart.

Heart chambers and heart valves

The heart has four chambers. The two ventricles (right and left) are muscular chambers that propel the blood out of the heart (the right ventricle to the lungs, and the left ventricle to all other organs). The two atria (right and left) hold the blood returning to the heart, and at just the right moment empty into the right and left ventricles.

The four heart valves (tricuspid, pulmonic, mitral and aortic) keep the blood moving in the right direction through the heart.

How the heart pumps blood

It is helpful to visualize the heart as two separate pumps, working in series – the right heart pump, and the left heart pump.

The right heart pump

Figure 1: The right heart pump consists of the right atrium (RA), tricuspid valve (TV), right ventricle (RV), pulmonic valve (PV), and pulmonary artery (PA).Poorly oxygenated blood returning to the heart from the body's organs enters the right atrium, and is stored there until the right atrium contracts.

Figure 2: When the right atrium contracts, the tricuspid valve opens, allowing the blood to enter the right ventricle.

Figure 3: Then, when the right ventricle contracts, the pulmonic valve opens, and the blood is propelled into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it picks up oxygen.

The left heart pump

The left heart pump consists of the left atrium (LA), mitral valve (MV), left ventricle (LV), aortic valve (AV), and aorta (Ao). Well oxygenated blood returning to the heart from the lungs enters the left atrium, and is stored there until the left atrium contracts.

The left heart pump (continued)

When the left atrium contracts, the mitral valve opens, allowing the blood to enter the left ventricle

The left heart pump (continued)

Then, when the left ventricle contracts, the aortic valve opens, and the blood is propelled into aorta, the main artery of the body. The aorta then carries the blood throughout the body.

Anatomy of the Normal Coronary Arteries

The coronary arteries carry blood to the heart muscle. Because the heart muscle is continuously working (as opposed to other muscles of the body, which are often at rest), it has a very high requirement for oxygenated blood. The coronary arteries are vitally important for supplying that blood, and allowing the heart to work normally.

As shown in the figure , two major coronary arteries arise from the aorta – the right coronary artery (RCA) and the left main artery (LM). The left main artery quickly branches into two large arteries – the left anterior descending artery (LAD) and the circumflex artery (Cx). Blockage in any of these major coronary arteries can damage large segments of heart muscle. Heart muscle death due to blockage in a coronary artery is referred to as a myocardial infarction, or heart attack.

The Cardiac Electrical System

The heart generates its own electrical signal, or impulse. This electrical impulse can be recorded by placing electrodes on the skin of the chest, thus producing the electrocardiogram (ECG, or EKG).

The heart’s electrical impulse arises in the upper portion of the right atrium and spreads across. As it spreads, it triggers the heart muscle to contract in a coordinated fashion. If the electrical signal becomes deranged in some way, the efficient pumping action of the heart may deteriorate, or stop altogether.

Figure 1: The components of the heart’s electrical system are illustrated here. From an electrical standpoint, the heart is divided into two portions – the atria, and the ventricles. Separating the atria from the ventricles is a non-muscular, fibrous “disc.” This disc (labeled AV disk in the figure,) prevents the passage of the electrical signal between the atria and the ventricles. In this figure, SN = sinus node; AVN = AV node; RA = right atrium; LA = left atrium; RV = right ventricle; LV = left ventricle.

The next figures illustrate how the electrical impulse spreads across the heart.

Figure 2: The electrical impulse originates in the sinus node. From there, it spreads across both atria, causing the atria to contract. As the electrical impulse passes through the atria, it generates the so-called “P” wave on the ECG. (The P wave is indicated by the solid purple line on the ECG below.)

Figure 3: When the wave of electricity reaches the AV disc, it is essentially abolished (that is, it does not pass across the AV disc to the ventricles), except in the specialized AV conduction system.

The Cardiac Electrical System 2

Figure 4: The specialized AV conduction system consists of the AV node (AVN), the His bundle, and the right and left bundle branches (RBB and LBB). The AV node conducts the electrical impulse very slowly, and passes it to the His bundle (pronounced “hiss”). The His bundle penetrates the AV disk, and passes the signal to the right and left bundle branches. The right and left bundle branches, in turn, send the electrical impulse to the right and left ventricles, respectively. (Note that the LBB itself splits into the left anterior fascicle (LAF) and the left posterior fascicle (LPF).)

Because the impulse travels only very slowly through the AV node, there is a pause in the electrical activity on the ECG, referred to as the PR interval. (The PR interval is indicated by the solid purple line on the ECG above. This “pause” in the action allows the atria to contract fully, emptying their blood into the ventricles before the ventricles begin to contract.)

The Cardiac Electrical System 3

Figure 5: This figure shows the electrical impulse spreading throughout the right and left ventricles, causing these chambers to contract. As the electrical signal travels through the ventricles, it generates the “QRS complex” on the ECG. The QRS complex is indicated by the solid purple line on the ECG below.

In this manner, the electrical system of the heart causes the heart muscle to contract, and causes it to contract in a coordinated manner, maximizing the efficiency of the beating heart.