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When it’s atrial fibrillation
For people who were told they have atrial fibrillation (AFib), people whose heart flutters, races or skips and who do not know why, and the people beside them. This page passes on, by name, what the National Heart, Lung, and Blood Institute (NHLBI) says: the signs that are a 911 call, what it feels like and the four types, how it is found, blood clots, stroke and blood thinners, the medicines that slow the heart or steady its rhythm, cardioversion, ablation and other procedures, day-to-day care, and what raises the risk. It builds the questions to ask at a visit. Take only what you need today.
A word with a dotted line under it, like this, opens its official definition, quoted from a U.S. government glossary.
Right now
- Call 911 for the signs of a stroke: sudden weakness, sudden trouble speaking, walking, or seeing, or sudden headache. NHLBI’s words: every minute matters.
- Call 911 for the symptoms of a heart attack, or if someone suddenly faints. For someone who has fainted and has no heartbeat, NHLBI says to look for a defibrillator nearby and follow the instructions.
- On a blood thinner? NHLBI says bleeding that will not stop after you apply pressure to a wound for 10 minutes is excessive, and it lists other signs of bleeding that are a 911 call. They are under “When to call 911” below.
- Do not stop a blood thinner or a heart medicine on your own. That sentence is ours; NHLBI says it is important that you continue your treatment. Ask the person who prescribed it first.
- Thinking about ending your life? Call or text 988, at any hour.
More help
- It might be a stroke or a heart attack: When it might be a stroke and When it might be a heart attack.
- Bleeding: When someone is bleeding.
- Keeping track: My medicines, Symptom diary and My emergency card.
- Before a visit: Get ready for your appointment.
- No insurance, a medicine or a bill you can’t pay: When you need a doctor and can’t pay, When you can’t afford your medicine and When a medical bill is too much.
- What often comes with it: When it’s high blood pressure, When it’s heart failure, When it’s high cholesterol and When blood sugar goes too low or too high.
- Alcohol, drugs and smoking: When drinking or drugs have become a problem and When you want to quit smoking.
- Looking after someone: When you’re caring for someone.
- All our free tools.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor, nurse, pharmacist or person living with atrial fibrillation has reviewed it. The facts were read on October 8, 2026 on the website of the National Heart, Lung, and Blood Institute, part of the National Institutes of Health (nhlbi.nih.gov: its atrial fibrillation pages on what it is, types, symptoms, diagnosis, causes and risk factors, treatment, and living with it, each marked “Last updated on November 30, 2022”). It is the only source of this guide. The page says when it is passing on the institute’s words, and what is marked “ours” is our own. What we left out or did not read: every medicine brand and amount; the names of the four individual medicines in the group called DOACs (we name warfarin and that group, because the institute’s follow-up advice differs between them, and otherwise only the kinds of medicine); any score for working out the risk of a stroke; the names of the consumer devices that record a heart rhythm; how each procedure is done and what recovery is like (we did not read the institute’s separate pages on cardioversion, ablation, pacemakers or heart surgery, or its pages on stroke, heart attack and cardiac arrest); its fact sheets and its DASH eating plan; where to get a free or low-cost test; prices; and anything about what Medicare, Medicaid or private insurance pay for. Advice you may have seen elsewhere, such as taking your own pulse each day or limiting coffee, is not on the pages we read, so it is not here: ask your provider. We called no number. It saves nothing and loads no tracking.