How Does the Heart Work?

It consists of three main structures. The pericardium is the thin outer lining surrounding and protecting the organ. The myocardium is the thick muscular middle layer that pumps blood when it contracts and squeezes. Finally, the endocardium is the thin, smooth membrane lining the chambers of the heart that makes up the surface of the valves.

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The heart has four interior chambers, two on the left and two on the right. The atria are the two small upper chambers, and the ventricles are the two larger lower chambers. The septum is the thin muscular wall separating the left chambers from the right. To remind your heart to keep pumping, the sinus node, a natural pacemaker, sends electrical signals throughout the heart.

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Though the heart is separated into two parts, they work together. The right side gets de-oxygenated blood that has already circulated through your body. It pumps this "used" blood to your lungs, where it is reinfused with oxygen. Then, the blood returns to the left side of the heart to be pumped back throughout your body. The heart has four valves that act as gates, opening and closing to keep the blood flowing in one direction. They work a little like one-way traffic lights. The valves on the right side of the heart are called the tricuspid and pulmonary valves, while the mitral and aortic valves are on the left side.

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A contraction of the heart muscle moves the blood, pushing it from the left side, through the aorta (the main artery exiting the heart) and into the arteries. The blood circulates through arteries that divide off into tiny blood vessels or capillaries. On their journey through the capillaries, blood has the opportunity to nourish every part of the body. The de-oxygenated blood returns via veins to the right side of your heart. To keep you alive, it needs a continuous supply of blood. The coronary arteries branch off from the aorta and spread along the exterior of the heart, supplying it with blood.

Cardiovascular diseases are conditions that affect the heart and circulatory system. They have various causes and risk factors. These disorders include

• heart attack
• congenital heart disease
• stroke
• angina
• inherited heart conditions
• vascular dementia
• diabetes

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There are many causes of circulatory diseases. Narrowed arteries can lead to strokes, heart attacks, or angina due to a slow build-up of fatty material (atheroma) along the blood vessel walls. In time, the arteries may clog, which interrupts their ability to deliver blood to the heart or brain. This can cause a stroke, heart attack or vascular dementia.

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Many heart and circulatory diseases have the same risk factors, including

• obesity
• drinking too much alcohol
• high blood pressure
• high cholesterol
• poorly managed diabetes
• smoking

Fortunately, there are many ways to turn the situation around and reduce your risk of heart and circulatory conditions. Many involve some lifestyle changes, but it's worth it for a strong, healthy heart.

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Blood is essential. It carries fresh oxygen from your lungs, delivers nutrients to body tissues, and removes waste products such as carbon dioxide. This sustains life and keeps your body functioning optimally. Put together end to end, the vast system of blood vessels in a single body is around 60,000 miles long -- long enough to wrap around the world twice. Thanks to the heart, your blood flows continuously throughout your body's blood vessels to make everything else possible.

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There are three types of blood vessels. Arteries begin with the aorta, the large artery exiting the heart. They carry oxygenated blood from the heart to the body's tissues. Arteries branch off over and over and eventually become tiny capillaries that carry blood into organs. Capillaries join arteries and veins. Their thin walls let oxygen, nutrients, carbon dioxide, and waste pass in and out of an organ's cells. Veins return blood back to the heart. This blood is laden with waste and low on oxygen. Veins become larger as they approach the heart, culminating in the superior vena cava, which brings blood from the head and arms to your heart, and the inferior vena cava that returns blood from the abdomen and legs.

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The heart lies under the rib cage, to the left of the sternum, between your lungs. The outside is made of muscle. Strong muscular walls squeeze to pump blood. On the surface, you can see coronary arteries that supply oxygen-rich blood to the heart muscle. The heart doesn't look like the artistic version we draw to express romantic notions. Instead, it is a fist-sized organ composed mostly of muscle tissue.