An arrhythmia is an irregular heart rhythm, meaning your heart beats too fast, too slow, or with an uneven pattern. A normal resting heart rate for adults falls between 60 and 100 beats per minute. When the electrical signals that coordinate each heartbeat malfunction or travel along the wrong path, the result is an arrhythmia. Some arrhythmias are harmless and barely noticeable, while others can be life-threatening.
How Your Heart’s Electrical System Works
Every heartbeat starts with a tiny electrical impulse generated by a cluster of cells called the SA node, located in the upper part of your heart. This signal spreads across the two upper chambers (atria), causing them to contract and push blood down into the lower chambers (ventricles). The signal then pauses briefly at a relay point called the AV node, giving the upper chambers time to fully empty. After that pause, the signal races through a network of specialized fibers in the ventricles, triggering them to contract and pump blood out to your lungs and the rest of your body.
Your nervous system adjusts the speed of this process constantly. When you’re exercising or stressed, your fight-or-flight response speeds up the SA node. When you’re resting or sleeping, the rest-and-digest system slows it down. An arrhythmia happens when something disrupts this sequence: the SA node fires too fast or too slow, the signal gets stuck in a loop, or an extra electrical impulse fires from the wrong location. If the SA node fails entirely, backup cells lower in the system can take over, but they typically produce a slower, less reliable rhythm.
Types of Arrhythmia
Arrhythmias fall into a few broad categories based on where they originate and how they affect heart rate.
Bradycardia
A resting heart rate below 60 beats per minute. This isn’t always a problem. Well-trained athletes can have resting rates near 40 beats per minute and feel perfectly fine. Bradycardia becomes a concern when it causes dizziness, fatigue, or fainting because the heart isn’t pumping enough blood to meet the body’s needs.
Tachycardia
A resting heart rate above 100 beats per minute. It can originate in the upper chambers (supraventricular tachycardia) or the lower chambers (ventricular tachycardia). Ventricular tachycardia is generally more dangerous because the ventricles are responsible for pumping blood to your organs. It can last just a few seconds or persist much longer, and sustained episodes require urgent medical attention.
Atrial Fibrillation
The most common type of arrhythmia. During atrial fibrillation (AFib), the upper chambers quiver chaotically at rates exceeding 400 beats per minute instead of contracting in an organized way. They fall completely out of sync with the lower chambers. A closely related condition, atrial flutter, drives the upper chambers at 250 to 350 beats per minute in a more organized but still abnormal pattern.
Premature Heartbeats
These feel like a skipped beat or a sudden thump in your chest. They happen when an electrical signal fires earlier than expected. Premature beats are extremely common, often harmless, and can occur in people with perfectly healthy hearts.
Common Symptoms
Many people with arrhythmias feel palpitations, often described as a fluttering, pounding, or racing sensation in the chest. Other common symptoms include dizziness, lightheadedness, shortness of breath, fatigue, chest pain, and a general feeling of weakness. You might also notice a reduced ability to exercise at your usual intensity.
Some arrhythmias produce no symptoms at all. AFib, for example, can go undetected for months or years. This is part of what makes it risky: even without symptoms, the irregular rhythm can allow blood to pool in the heart and form clots, which significantly raises the risk of stroke.
What Triggers an Arrhythmia
Arrhythmias often have an underlying cause, such as heart disease, high blood pressure, or a structural problem with the heart. But even in people who already have a risk factor, specific triggers can set off an episode. The National Heart, Lung, and Blood Institute identifies several common ones:
- Caffeine and stimulant drugs, which can push the heart’s electrical system to fire more rapidly
- Strong emotional stress, anxiety, anger, pain, or sudden surprise
- Dehydration and low levels of electrolytes like potassium, magnesium, or calcium
- Blood sugar levels that are too high or too low
- Intense physical activity, particularly if you’re not conditioned for it
- Vomiting or heavy coughing, which can stimulate the nerve pathways that influence heart rhythm
Not everyone with these triggers will develop an arrhythmia. They tend to matter most when the heart’s electrical system is already vulnerable due to age, genetics, or existing heart conditions.
Why Arrhythmias Can Be Dangerous
The biggest concern with certain arrhythmias, particularly AFib, is stroke. When the upper chambers don’t contract properly, blood can pool and form clots. If a clot travels to the brain, it blocks blood flow and causes a stroke. People with heart failure are two to three times more likely to suffer a stroke than those without it, and the risk spikes dramatically in the first 30 days after a heart failure diagnosis.
Arrhythmias can also weaken the heart over time. A heart that beats too fast for too long has to work harder than it should, which can gradually lead to heart failure. Ventricular fibrillation, a chaotic rhythm in the lower chambers, is the most immediately dangerous arrhythmia because the heart essentially stops pumping blood. Without treatment within minutes, it’s fatal.
How Arrhythmias Are Diagnosed
A standard electrocardiogram (ECG or EKG) records your heart’s electrical activity, but only for a few seconds while you’re in the clinic. If your arrhythmia comes and goes, a brief snapshot might miss it entirely. That’s where portable monitors come in.
A Holter monitor is a small device you wear that records your heart rhythm continuously for 24 to 48 hours. If your symptoms happen less frequently, an event monitor may be more useful. It doesn’t record continuously. Instead, it either records when you press a button during symptoms or automatically starts recording when it detects an abnormal rhythm. Event monitors can be worn for a month or longer, making them better at catching arrhythmias that strike unpredictably.
Consumer smartwatches have also become surprisingly capable screening tools. Two large meta-analyses found that smartwatches and smartphone-paired devices detect atrial fibrillation with 96% sensitivity and 94% specificity, performing comparably to medical-grade devices. A smartwatch alert isn’t a diagnosis on its own, but it can be a valuable early signal that prompts proper testing.
Treatment Options
Treatment depends entirely on the type of arrhythmia, how severe it is, and whether it causes symptoms or poses a risk of complications. Minor arrhythmias with no symptoms sometimes need no treatment at all, just monitoring.
Medications are often the first step for arrhythmias that need treatment. Beta-blockers slow the heart by reducing the effect of stress hormones on the heart’s pacemaker cells. Calcium channel blockers work similarly, slowing conduction through the heart. Other medications target the electrical channels in heart cells directly, either stabilizing them to prevent extra signals or adjusting how quickly cells recover between beats. For people with AFib, blood thinners are frequently prescribed to reduce the risk of clot formation and stroke, even if the rhythm itself isn’t causing noticeable symptoms.
When medications don’t work well enough or cause intolerable side effects, catheter ablation is a common next step. During this procedure, a thin tube is threaded through a blood vessel to the heart, and the small area of tissue responsible for the abnormal signal is destroyed using heat or cold. Ablation is particularly effective for supraventricular tachycardias and atrial flutter, and it’s used for AFib when medications have failed to control symptoms.
For slow arrhythmias, a pacemaker can be implanted to deliver electrical impulses that keep the heart beating at a normal rate. For dangerous fast rhythms, an implantable cardioverter-defibrillator (ICD) monitors the heart continuously and delivers a shock if it detects a life-threatening rhythm like ventricular tachycardia or ventricular fibrillation. Both devices are small, placed under the skin near the collarbone, and last for years before the battery needs replacing.
Living With an Arrhythmia
Many arrhythmias are manageable with the right combination of lifestyle adjustments and medical treatment. Reducing known triggers, like limiting caffeine, managing stress, staying hydrated, and keeping electrolyte levels balanced through a varied diet, can reduce how often episodes occur. Regular physical activity is generally beneficial for heart health, but if you’ve been diagnosed with an arrhythmia, the type and intensity of exercise that’s appropriate depends on your specific condition.
Tracking your symptoms helps. Note when episodes happen, what you were doing, and how long they lasted. This information is genuinely useful for your cardiologist in choosing or adjusting treatment. If you wear a smartwatch with ECG capability, saving those recordings can provide your doctor with data that would otherwise require a clinic visit to capture.