Lifestyle

A Fluttering or Racing Heartbeat Can Be a Sign of AFib. The Most Common Symptom Is Tiredness

By Erica Coleman · October 26, 2026

A heartbeat that suddenly flutters, pounds or races for no clear reason is the symptom most people connect with atrial fibrillation. The sign that shows up most often is far less dramatic.

According to the National Heart, Lung, and Blood Institute, the most common symptom of atrial fibrillation is fatigue, or extreme tiredness. The institute also says AFib often occurs with no symptoms at all, and that people who do have symptoms may notice them only occasionally.

Atrial fibrillation, often called AFib, is an irregular and often very rapid heart rhythm, Mayo Clinic explains. The heart’s upper chambers beat chaotically and out of sync with the lower chambers. The NHLBI says that when this happens, the lower chambers do not fill completely or pump enough blood to the lungs and body. The institute adds that the risk increases as you get older, especially after age 65.

These are the signs listed by the NHLBI, Mayo Clinic, the American Heart Association and the Centers for Disease Control and Prevention.

Fluttering, pounding or racing heartbeat. Mayo Clinic calls a fast, fluttering or pounding heartbeat palpitations. The NHLBI describes the feeling that the heart is skipping a beat or beating too hard or too fast. The American Heart Association lists fluttering or “thumping” in the chest among AFib symptoms.

Tiredness and weakness. Along with fatigue, Mayo Clinic and the heart association both list weakness. The heart association also lists fatigue when exercising, and Mayo Clinic lists a reduced ability to exercise.

Shortness of breath. All four sources list it. The NHLBI describes difficulty breathing, especially when lying down or when exercising.

Dizziness, lightheadedness or fainting. Each source lists dizziness or lightheadedness. The NHLBI also lists fainting, and the heart association includes faintness or confusion.

Chest pain. Chest pain appears on all four lists. Mayo Clinic advises getting emergency medical help right away for chest pain because it could mean a heart attack, and the heart association calls chest pain or pressure a medical emergency that warrants a call to 911.

Sweating and anxiety. The heart association lists sweating, and it pairs shortness of breath with anxiety.

The biggest concern is stroke. Mayo Clinic says AFib can lead to blood clots in the heart, and the CDC says AFib increases a person’s risk for stroke. The heart association says that even with no symptoms, a person with AFib is up to nearly five times more likely to have a stroke than someone who doesn’t have it.

For that reason, the heart association urges people with AFib to know the warning signs of stroke. Its B.E. F.A.S.T. checklist covers a sudden loss of balance, sudden changes in vision, one side of the face drooping, weakness in one arm, and slurred or difficult speech. If any of these appear, even if they go away, it says to call 911.

The CDC lists risk factors that include advancing age, high blood pressure, obesity, diabetes, heart failure, an overactive thyroid, chronic kidney disease, moderate to heavy alcohol use and smoking. Mayo Clinic adds sleep apnea and notes that certain cough and cold remedies bought without a prescription can cause irregular heartbeats.

Mayo Clinic advises anyone with symptoms of AFib to make an appointment for a health checkup. The NHLBI suggests keeping track of when and how often symptoms occur and what they feel like, since those details help providers make a diagnosis. Treatment can include medicines to control the heart’s rhythm and rate, along with blood-thinning medicine to prevent clots and reduce stroke risk, according to the CDC.

This article is for general information and is not medical advice. Talk with your doctor about any symptoms, and call 911 for chest pain or signs of a stroke. This article was produced with the assistance of AI and fact-checked against the sources cited by LightWave Reports.