What is the heart?
The heart is a muscular organ that continuously pumps oxygen and blood throughout your body. It is, essentially, what sustains life. The average heart beats 100,000 times per day, pumping approximately 2,000 gallons of blood through your body.
A healthy heart supplies adequate amounts of blood to areas of the body at the rate it's needed. Injury and disease can prevent the heart from adequately working and may increase the risk of additional health complications.
Anatomy of the Heart
You've likely heard the rhythmic cadence "lub-DUB, lub-DUB, lub-DUB" of a heartbeat heard through a stethoscope. That's the sound of blood pumping into and out of your heart. While it may seem like a simple task, many intricate mechanisms actually get your heart from the "lub" to the "DUB" in precise, lightning-fast motion.
The heart, located centrally between the right and left lungs, is protected by your ribcage. The normal, healthy adult heart is the size of an average adult's clenched fist. However, some diseases and conditions can cause the heart to grow significantly larger.
How Blood Travels
A heart has four chambers—the two upper chambers are called the atria, and the two lower chambers are called the ventricles. The atria receive blood, and the ventricles expel, or pump out, blood from the heart into the circulatory system.
A network of blood vessels—arteries, capillaries, and veins—carries blood around the body. The two largest veins in the body, called the venae cavae, carry oxygen-depleted blood from the body, back to the heart. The superior vena cava is responsible for bringing in blood from the upper part of the body—the head, chest, necks, and arms. The inferior vena cava is responsible for blood flow from the lower part of the body.
Your heart has a series of valves, or doors, which keep the blood flowing in one direction. On both sides of the heart, a valve opens, allowing blood to move from the atrium into the ventricle. And then another valve at the bottom of each ventricle opens and closes to pump blood into the body. The valves in a healthy heart work in perfect harmony with one another, opening and closing precisely so blood flow is even and rhythmic.
Once your organs and tissues have removed the oxygen and nutrients from the blood, it is pumped through the body to the venae cavae, into your heart's right atrium, and then to the right ventricle. From the right ventricle, pulmonary arteries carry the blood to your lungs. Waste products, such as carbon dioxide, are exchanged for oxygen through tiny capillaries. The oxygen-rich blood then passes back into the larger pulmonary veins and travels back to the heart where it enters the left atrium. Once there, it flows into the left ventricle and is pumped into the body through the aorta.
What makes a heartbeat?
A heartbeat can be summarized into two processes: contraction and relaxation. The diastole is the relaxation of the heart. The systole is the contraction. When the heart relaxes (during diastole), the atria and ventricles fill with blood. The atria then contracts (atrial systole) and pumps blood into the ventricles. (Here, the atria relax again and begin to fill with blood to start the process again). Then your ventricles contract (ventricular systole) and pump blood into the body.
The average adult's heart repeats this pattern 60 to 100 times per minute. Any interruption in this flow is called an arrhythmia.
A-fib and Your Heart
In a normal heart, the functions of the atria and ventricles are perfectly timed and coordinated. But sometimes the heart beats irregularly—this is called an arrhythmia.
The heart of a person with atrial fibrillation beats very rapidly; sometimes as fast as 240 to 350 beats per minute. (The average heart beats only 60 to 100 times per minute). The atria are moving so rapidly they aren't able to fully contract. Instead, they quiver, or fibrillate.
For some patients, this sensation is noticeable, and it can even cause some discomfort. But the pulse usually remains steady. However, some of these increased atrial beats can be transferred to the ventricles, which may cause an increased pulse.
A-fib affects mainly people over 60, and the risk of developing this arrhythmia increases with age, mostly due to the wear and aging an older heart experiences. The chances of developing a-fib are also increased if you have or have had high blood pressure, heart disease, or other heart problems. Although it is rarely life threatening, a-fib can be dangerous; if left untreated, it can cause more serious conditions, such as stroke or heart failure.