Atrial fibrillation, commonly called AFib, is an irregular and often rapid heart rhythm caused by chaotic electrical signals in the upper chambers of the heart. Instead of beating in a steady, coordinated pattern, the atria quiver erratically, which can allow blood to pool, form clots, and potentially travel to the brain. Around 52.5 million people worldwide have AFib, a number that has more than doubled since 1990.
How a Normal Heartbeat Goes Wrong
In a healthy heart, each beat starts with a single electrical impulse from a natural pacemaker in the right atrium. That signal travels through both upper chambers in an orderly wave, causing them to contract and push blood into the lower chambers. From there, the signal moves down to the ventricles, which pump blood out to the lungs and body. The whole sequence is tightly coordinated.
In AFib, the process breaks down at the very start. Instead of one clean signal, multiple electrical impulses fire at once from locations that aren’t supposed to generate them. The vast majority of these rogue signals originate in the pulmonary veins, the blood vessels where oxygenated blood returns from the lungs to the heart. The muscle cells in this area have unusual electrical properties: a lower resting charge, shorter electrical pulses, and a greater tendency to fire on their own. That combination makes them prone to misfiring.
Once those erratic signals flood the atria, the upper chambers can’t contract in a coordinated way. They quiver at rates of 300 to 600 times per minute. The lower chambers try to keep up, but the electrical gatekeeper between the atria and ventricles (the AV node) filters the signals irregularly, producing the hallmark of AFib: a heart rate that feels fast and completely unpredictable.
Why AFib Tends to Get Worse Over Time
One of the most important things to understand about AFib is that it changes the heart in ways that make more AFib likely. This process happens on two levels.
First, the electrical wiring of the atria remodels itself. During AFib episodes, the heart’s electrical recovery period shortens, meaning cells become ready to fire again faster than normal. At the same time, the proteins that carry electrical signals between cells (called gap junctions) change in number and location. This creates patchwork areas where signals slow down, speed up, or travel in only one direction, setting the stage for electrical loops that circle back on themselves and sustain the irregular rhythm.
Second, the physical structure of the atria changes. Scar tissue (fibrosis) gradually replaces normal heart muscle. These fibrosis deposits force electrical signals to zigzag around obstacles rather than flowing smoothly, which encourages more electrical loops and makes the rhythm harder to correct. This is the biological basis for the clinical observation that AFib tends to progress: early episodes may stop on their own, but over time, the remodeled heart becomes increasingly resistant to returning to a normal rhythm.
Types of AFib
AFib is classified by how long episodes last and whether they resolve on their own:
- Paroxysmal AFib comes and goes. Episodes usually stop within 24 hours but can last up to a week. At this stage, the problem is primarily electrical, driven by those rogue signals from the pulmonary veins.
- Persistent AFib lasts longer than a week and typically requires medical intervention to restore a normal rhythm. Both electrical triggers and structural changes in the atria play a role.
- Long-standing persistent AFib continues for more than a year without returning to normal.
These categories matter because they guide treatment decisions. Paroxysmal AFib responds better to procedures that target the pulmonary veins, while persistent forms often involve more widespread changes in the heart tissue.
What AFib Feels Like
The experience varies widely. Some people feel a racing, fluttering, or pounding sensation in the chest. Others notice shortness of breath, lightheadedness, fatigue, or a general feeling that something is off. Episodes can last minutes or days.
About 27% of people with AFib have no symptoms at all. This “silent” AFib is not harmless. Studies show that people with asymptomatic AFib face the same risks of stroke and other complications as those who feel every episode, and they may actually be at higher risk of the condition progressing because it goes undetected and untreated longer.
How AFib Causes Strokes
The stroke risk from AFib is specific and mechanical. When the atria quiver instead of contracting fully, blood doesn’t empty completely with each beat. It lingers, particularly in a small pouch on the left atrium called the left atrial appendage. This pouch has a complex internal shape with ridges and crevices where sluggish blood can stagnate. About 90% of blood clots that form in the hearts of AFib patients originate in this one structure.
If a clot breaks free, it travels through the left side of the heart, into the aorta, and up into the arteries supplying the brain. The result is an ischemic stroke. Doctors estimate stroke risk using a scoring system called CHA2DS2-VASc, which adds points for heart failure, high blood pressure, age (especially over 75), diabetes, prior stroke, vascular disease, and female sex. A score of 2 or higher generally means the stroke risk is high enough to warrant blood-thinning medication.
How AFib Is Diagnosed
The standard diagnostic tool is an electrocardiogram (ECG or EKG), a simple test that records the heart’s electrical activity through sensors on the skin. Two features confirm AFib on an ECG: the absence of normal P waves (the small blips that represent an organized atrial contraction), replaced by rapid, irregular “fibrillatory waves,” and an irregular spacing between heartbeats. The rhythm is not just fast; it is unpredictably irregular, which distinguishes AFib from other rapid heart rhythms.
Because paroxysmal AFib comes and goes, a standard ECG taken during a normal rhythm will look completely fine. In that case, longer monitoring with wearable devices that track heart rhythm over days or weeks can catch episodes that would otherwise be missed.
Treatment: Controlling Rate vs. Restoring Rhythm
Treatment for AFib generally follows two strategies, and the choice depends on symptoms, how long the AFib has been present, and other health conditions.
Rate control aims to slow the heart rate to a comfortable level without trying to fix the rhythm itself. This is often the first approach, particularly when AFib is a consequence of another condition like an infection, or when restoring normal rhythm has already been tried without success. Medications that slow how quickly electrical signals pass through the AV node bring the heart rate down even though the atria continue to fibrillate.
Rhythm control aims to restore and maintain a normal heart rhythm. This can involve medications that suppress the abnormal electrical activity, electrical cardioversion (a brief, controlled shock that resets the heart’s rhythm), or catheter ablation. In ablation, a catheter is threaded through a blood vessel to the heart, where it delivers energy to create small scars around the pulmonary veins, electrically isolating the tissue that generates the rogue signals. Ablation reduces AFib recurrences compared to medication alone, but 20% to 40% of patients experience a return of the arrhythmia, particularly those with more advanced structural remodeling.
Regardless of which strategy is chosen, most AFib patients with elevated stroke risk also take blood-thinning medication to prevent clot formation in the left atrial appendage.
Lifestyle Changes That Reduce AFib Episodes
Several modifiable risk factors have a measurable impact on AFib burden. Weight loss is the most powerful. In one study, patients who lost and maintained at least 10% of their body weight were six times more likely to remain free of arrhythmia compared to those who lost less than 3% or gained weight. Among those with persistent AFib who achieved that level of weight loss, 88% improved to either occasional episodes or no AFib at all.
Alcohol reduction also makes a significant difference. Among regular drinkers (10 or more drinks per week) who stopped, AFib recurred in 53% over six months, compared to 73% of those who kept drinking, with the abstinence group also experiencing longer gaps between episodes and a lower overall AFib burden. Moderate drinking of one or fewer drinks per day for women, and two or fewer for men, has not shown increased risk.
A reasonable set of initial goals for reducing AFib burden includes a 10% reduction in body weight, maintaining a BMI below 27, and increasing physical fitness by at least two metabolic equivalents, roughly the difference between being sedentary and being able to walk briskly without difficulty. These changes don’t just improve symptoms. They alter the underlying structural and electrical remodeling that drives the condition forward.