What Is a Dangerous Heart Rate With AFib?

Atrial fibrillation (AFib) is an irregular heartbeat that happens when the electrical signal in the heart gets scrambled. Most of the time, it makes your heart beat faster than normal. Many people experience that as palpitations. But some people don’t notice that they are in AFib, even if their heart is beating too fast. So what’s considered a dangerously high heart rate with AFib? We’ll explain what you need to know, and what you can do about it.

What is a dangerous heart rate with AFib?

A dangerous heart rate with AFib is different for everyone. Some people will have problems when they are in AFib even if their heart rate is in a normal range. But for most people, if the heart rate stays above 120 beats per minute, that can put extra stress on the heart. That’s especially true for people who are older than 65 years, or those with other health conditions.  

A normal resting heart rate is usually between 60 and 100 beats per minute. But with AFib, the rhythm isn’t steady. If you have AFib and you’re not on medication, your heart rate will likely be faster than normal. 

With AFib, it can be OK to have a slightly faster heart rate. Research shows that keeping your average heart rate at between 60 and 110 beats per minute is usually best when you have AFib. Sometimes the heart rate will naturally stay in that range. But most people with AFib will need medication to keep the heart rate under control.

In general, if your heart rate is consistently over 120 beats per minute, you should get medical care right away. This often means going to the emergency room, especially if you feel unwell or have symptoms of chest pain and shortness of breath. In some cases, your cardiologist may be able to guide you on what to do next.

Why does AFib lead to a high heart rate?

The heart’s natural pacemaker — called the sinus node — is located at the top of the heart. It’s a small piece of electrical tissue that sends a signal to the rest of the heart telling it to beat. When the heart is functioning normally, the heartbeat is organized and steady. 

In AFib, this sinus node is no longer in control. The top chambers of the heart — called the atria — generate abnormal electrical signals. These abnormal signals override the sinus node so that it can no longer control the rest of the heart. These mixed-up signals are very fast. This means that the heart muscle is receiving signals to beat faster than normal. If you look at the heart when it’s in AFib (like with an echocardiogram), you can see the atria quivering instead of squeezing.

Why is an elevated heart rate with AFib so dangerous?

A fast heart rate with AFib can cause symptoms like:

• Fatigue

• Chest pain

• Shortness of breath

• Dizziness

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These symptoms happen because the heart is working much harder than it should. When the heart beats too fast, it doesn’t have enough time to relax and fill with blood between each beat. If this continues for many hours or days, it can weaken the heart and cause heart failure.

It’s also important to know that AFib increases your risk for a stroke regardless of your heart rate. When the upper chambers are quivering, instead of squeezing, not all of the blood moves forward with each heartbeat. This blood can pool in the atria and form clots. If a clot travels to the brain, it can cause a stroke. Because of this risk, many people with AFib need to take blood thinners. Your healthcare team will help decide if this is right for you based on your personal risk factors.

What can you do to keep a low heart rate with AFib?

Some lifestyle changes can help keep the heart rate lower in AFib, and may even reduce how often AFib episodes happen. These include:

• Limiting alcohol

• Managing stress

• Getting treatment for sleep apnea, if needed

• Staying active with moderate exercise

• Maintaining a healthy and balanced weight

• Avoiding dehydration 

But to keep a low heart rate with AFib, most people need to take medication:

• Some medications, like beta blockers and certain calcium channel blockers, slow down your heart rate.

• Other medications, called antiarrhythmic medications, help keep you from going into AFib.

Some AFib medications, like amiodarone, can do both things. Other times, a combination of medications is needed. What may work best depends on your age and other risk factors. Each medication has potential benefits and side effects. So the choice of medications is a decision that you’ll make with your cardiologist.  

In some cases, a procedure called an ablation may be recommended. It’s a procedure that destroys a small part of the heart that’s causing the abnormal electrical signals. There are two main types of ablations:

• One type of ablation helps prevent the heart from beating too fast but doesn’t stop AFib. 

• Another type of ablation procedures are designed to reduce episodes or even eliminate AFib. 

Ablations are done by a special type of cardiologist called an electrophysiologist (EP). Ablation isn’t right for everyone, so this is another decision to discuss with your cardiologist or EP.

In some cases, people with AFib may have a slow heart rate, even if they aren’t taking any heart medications. This can happen when there are problems throughout the heart’s electrical system. If the heart rate is too slow (usually under 50 beats per minute), a pacemaker may be needed to help keep the heart beating at a safe rate. 

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Written by:

Sarah A. Samaan, MD

Sarah Samaan, MD, FACC, FACP, FASE is a board-certified cardiologist who practiced clinical cardiology for nearly 30 years. She is a member of the American College of Cardiology and the American College of Physicians, among others.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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