Learn About AFib and Irregular Heart Rhythms

What Atrial Fibrillation Is and How the Heart Normally Works

To understand atrial fibrillation (AFib), it helps to know how a healthy heart beats. Your heart is a muscle about the size of your fist that pumps blood throughout your body. It has four chambers: two upper chambers called atria and two lower chambers called ventricles. The right side receives oxygen-poor blood from your body and sends it to the lungs. The left side receives oxygen-rich blood from the lungs and pumps it out to your body.

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A normal heartbeat follows an electrical pattern. An electrical signal starts in a spot called the sinoatrial node (SA node), which acts like your heart's natural pacemaker. This signal travels across the atria, causing them to squeeze and push blood down into the ventricles. The signal then reaches the atrioventricular node (AV node), which acts as a gateway, and travels into the ventricles, causing them to squeeze and push blood out of the heart. This coordinated electrical activity creates a regular rhythm—usually between 60 and 100 beats per minute at rest.

Atrial fibrillation happens when something disrupts this normal electrical pattern in the atria. Instead of one organized signal, the atria receive many chaotic electrical signals all at once. This causes the atrial muscle fibers to twitch or quiver rapidly and irregularly—sometimes at rates of 300 to 400 times per minute. Because these signals are disorganized, the atria cannot squeeze effectively to push blood into the ventricles. The ventricles respond unpredictably, causing your heartbeat to become irregular and often faster than normal.

The result is a heart rhythm that is not steady. You might feel your heart skip a beat, race suddenly, or flutter. Blood may pool in the atria instead of flowing smoothly, which creates a different set of risks. About 2.7 million Americans currently live with AFib, and it becomes more common with age.

Practical takeaway: AFib is an irregular rhythm caused by chaotic electrical signals in the heart's upper chambers. Understanding this basic mechanism helps you recognize why AFib requires ongoing monitoring and why certain treatments aim to slow the heart rate or restore regular rhythm.

Common Symptoms and When to Seek Medical Attention

The symptoms of atrial fibrillation vary widely from person to person. Some people experience noticeable symptoms, while others have AFib without feeling anything at all—a situation called asymptomatic AFib that may only be discovered during a routine medical visit or test.

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When symptoms do occur, the most common is a sensation of heart palpitations. This means you become aware of your heartbeat, which normally you don't notice. People describe palpitations as a fluttering feeling, a racing heart, or a skipping sensation in the chest. One person might feel their heart "flip-flopping" in their chest; another might describe it as a rapid drumming or pounding. The sensation might come and go, lasting from a few seconds to several hours.

Other symptoms that can accompany AFib include shortness of breath, dizziness or lightheadedness, unusual tiredness or weakness, and chest discomfort or pressure. Some people feel anxious during episodes, which can make the experience more distressing. Chest discomfort is concerning and requires attention—it can feel like pressure, tightness, or pain, and it's different from the palpitation sensation itself.

Seek immediate medical attention if you experience chest pain or pressure, severe shortness of breath, fainting or loss of consciousness, or severe dizziness that prevents you from standing safely. These symptoms could indicate a serious condition requiring urgent evaluation. Additionally, if you experience palpitations for the first time, or if they feel different than usual, contact a doctor. If you've been told you have AFib and your symptoms suddenly worsen or change character, medical evaluation is warranted.

Keep in mind that not all irregular heartbeats are AFib. Other arrhythmias exist, and only a doctor can diagnose your condition through examination and testing. Some people have occasional AFib episodes (paroxysmal AFib), while others have it continuously (persistent AFib). The pattern of your symptoms may vary depending on which type you have.

Practical takeaway: Document what you feel during irregular heartbeat episodes—the type of sensation, how long it lasts, what you were doing when it started, and whether you had other symptoms. This information helps your doctor understand your condition and track whether your symptoms change over time.

Risk Factors That Make AFib More Likely

Certain conditions and life circumstances increase the likelihood of developing atrial fibrillation. Age is the most significant factor. AFib is rare in people under 40, but the risk rises substantially after age 65. Research shows that roughly 9% of people over age 65 have AFib. This doesn't mean it's inevitable—many older adults never develop it—but the risk is much higher than in younger populations.

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Heart disease is a major risk factor. People who have experienced a heart attack, have heart valve problems, or suffer from heart failure face higher AFib risk. High blood pressure (hypertension) is another strong predictor. Chronic high blood pressure causes the heart muscle to thicken and stiffen, which disrupts normal electrical signaling. This is one reason controlling blood pressure is so important. Diabetes also increases AFib risk, partly because high blood sugar damages blood vessels and heart tissue over time.

Thyroid disorders, particularly an overactive thyroid (hyperthyroidism), can trigger AFib. When the thyroid produces too much hormone, it speeds up metabolism and heart rate, sometimes causing irregular rhythms. Obesity places stress on the heart and increases inflammation, both of which contribute to AFib development. Sleep apnea—a condition where breathing repeatedly stops and starts during sleep—is increasingly recognized as an AFib risk factor, possibly because it causes drops in blood oxygen levels.

Chronic lung disease, kidney disease, and excessive alcohol consumption also raise AFib risk. Binge drinking, even in people who don't drink regularly, can trigger episodes of AFib (sometimes called "holiday heart syndrome"). Certain medications and stimulant overuse, including excessive caffeine, may trigger AFib in susceptible people. Stress and illness can also precipitate episodes.

Some people have a family history of AFib, suggesting a genetic component. Having a parent or sibling with AFib makes it somewhat more likely you'll develop it too, though it's not a certainty. Understanding your personal risk factors helps you make informed decisions about monitoring and prevention efforts.

Practical takeaway: Review the risk factors listed above against your own health history. Those with multiple risk factors may benefit from more frequent heart health monitoring. Managing modifiable risk factors—like blood pressure, weight, sleep apnea, and alcohol intake—may lower your AFib risk.

How Doctors Diagnose AFib Through Testing

Diagnosing atrial fibrillation usually starts with a doctor listening to your heart with a stethoscope during a physical exam. An irregular rhythm raises suspicion, but the most important test is an electrocardiogram (EKG or ECG). This simple, painless test records the electrical activity of your heart by placing small sticker-like electrodes on your chest, arms, and legs. The machine creates a paper printout or digital image showing the heart's electrical patterns. An EKG taken during an AFib episode clearly shows the chaotic electrical activity characteristic of atrial fibrillation.

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The challenge is that many people don't experience AFib constantly. Your heart might be in a normal rhythm when you visit the doctor's office, meaning a single EKG might look normal even though you have AFib. To capture irregular episodes, doctors often use extended monitoring. A Holter monitor is a portable EKG device you wear for 24 to 48 hours while going about your daily activities. An event recorder is worn longer—sometimes for weeks or months—and only records when you press a button because you're feeling symptoms, or it may detect irregular rhythms automatically.

An echocardiogram uses ultrasound waves to create moving pictures of your heart. This test reveals the size and shape of the heart chambers, how well the heart pumps blood, and whether the heart valves are working properly. It can identify structural problems that might cause or worsen AFib. Blood tests may also be ordered to check thyroid function, kidney function, and electrolytes—all factors that influence