An arrhythmia is any heartbeat that doesn’t follow the normal rhythm. Your heart might beat too fast, too slow, or in an irregular pattern. A normal resting heart rate falls between 60 and 100 beats per minute, and your heart’s internal electrical system is responsible for keeping that rhythm steady. When something disrupts those electrical signals, the result is an arrhythmia.
Some arrhythmias are so mild you never notice them. Others cause noticeable symptoms like palpitations or dizziness. In rare but serious cases, an arrhythmia can be life-threatening. Understanding what’s happening inside your heart, and what the different types look and feel like, can help you make sense of a diagnosis or know when something needs attention.
How Your Heart Keeps a Rhythm
Your heart has its own built-in pacemaker: a small cluster of cells called the SA node, located in the upper right chamber. This node fires an electrical impulse that triggers each heartbeat. The signal travels to a second relay point called the AV node, near the center of the heart, which pauses the signal for a fraction of a second. That tiny delay is intentional. It gives the upper chambers time to finish pushing blood down into the lower chambers before those lower chambers contract.
From the AV node, the signal races through a network of specialized fibers in the walls of the lower chambers, causing them to squeeze and pump blood out to the lungs and the rest of the body. This entire sequence, from the SA node’s initial spark to the full contraction of the lower chambers, happens in less than a second and repeats roughly 100,000 times a day. An arrhythmia occurs when any part of this electrical pathway misfires, gets blocked, or generates signals from the wrong location.
Types of Arrhythmias
Arrhythmias are broadly grouped by whether the heart beats too slowly, too quickly, or chaotically.
Bradycardia is a resting heart rate below 60 beats per minute. For well-trained athletes, this can be completely normal. For others, it may mean the heart’s electrical signals are being delayed or blocked, which can cause fatigue, dizziness, or fainting if the heart isn’t pumping enough blood to meet the body’s needs.
Tachycardia is a resting heart rate above 100 beats per minute. It can originate in either the upper or lower chambers and ranges from mildly uncomfortable to dangerous, depending on the cause and how fast the heart is beating.
Atrial fibrillation (AFib) is the most common type of arrhythmia, affecting an estimated 52.5 million people worldwide. In AFib, the upper chambers fire chaotically, sometimes exceeding 400 beats per minute. The upper and lower chambers fall out of sync, so the lower chambers don’t fill with blood properly and can’t pump it efficiently to the lungs and body. AFib also raises the risk of blood clots forming in the heart, which can travel to the brain and cause a stroke.
Ventricular fibrillation (VFib) is the most dangerous type. The lower chambers quiver instead of pumping, which means blood effectively stops flowing. Without emergency treatment, VFib leads to cardiac arrest and death within minutes.
What an Arrhythmia Feels Like
Many arrhythmias produce no symptoms at all and are only discovered during a routine exam or an unrelated test. When symptoms do appear, the most common sensation is palpitations: a feeling that your heart is fluttering, pounding, skipping beats, or racing. You might also notice pauses between heartbeats that feel unsettling.
Beyond palpitations, arrhythmias can cause dizziness, lightheadedness, fainting, chest discomfort, shortness of breath, unusual fatigue, and a general sense of anxiety or confusion. Some people experience gasping or difficulty breathing during sleep. The severity of symptoms often depends on how much the arrhythmia reduces your heart’s ability to pump blood. A brief episode of a fast heartbeat might feel like a flutter in your chest that passes in seconds, while a sustained arrhythmia can leave you feeling weak and winded.
Common Causes and Triggers
Arrhythmias can develop for many reasons, and sometimes no clear cause is found. Several factors raise the risk:
- High blood pressure increases the risk of coronary artery disease, which in turn makes arrhythmias more likely.
- Electrolyte imbalances directly affect the heart’s electrical signaling. Potassium, magnesium, calcium, and sodium all play a role in generating and conducting those signals. When levels are too high or too low, from dehydration, medication side effects, or other causes, the rhythm can become unstable.
- Sleep apnea stresses the heart by repeatedly cutting off its oxygen supply during sleep, which can trigger slow or irregular heartbeats, including AFib.
- Genetics play a role in some arrhythmias. If a parent or close relative has one, your own risk is higher.
- Other health conditions such as heart failure, diabetes, and thyroid disease are all associated with increased arrhythmia risk, particularly as people age.
Certain medications, including some drugs for high blood pressure and mental health conditions, can also contribute. Aging itself is a significant factor, partly because older adults are more likely to have the underlying conditions listed above.
How Arrhythmias Are Diagnosed
The most common test is an electrocardiogram (ECG or EKG), which records the heart’s electrical activity through sensors placed on the skin. It’s quick, painless, and can reveal abnormal rhythms in real time. Sometimes a doctor will order an ECG during a stress test, while the heart is working hard, to catch problems that only surface during exertion.
Because many arrhythmias come and go, a single ECG might miss them. In those cases, portable monitors can track your heart rhythm over a longer period while you go about your daily life. A Holter monitor, worn outside the body, typically records for 24 to 48 hours. For arrhythmias that happen infrequently, a tiny implantable loop recorder can be placed just under the skin and worn for months, automatically transmitting data to your doctor’s office. This is especially useful for people who have unexplained fainting spells or rare palpitations.
Blood tests check for underlying causes like electrolyte imbalances or thyroid problems. Heart imaging with CT scans or MRI can reveal structural issues, scar tissue, or problems with how the chambers are functioning. Genetic testing is available for arrhythmias suspected to run in families. In some cases, doctors use an electrophysiology study, where a thin wire is threaded through a blood vessel to the heart to directly map and trigger abnormal electrical pathways. This test both pinpoints the problem and helps determine whether a specific treatment will work.
Treatment Options
Treatment depends on the type of arrhythmia, its severity, and whether it poses a risk of stroke or cardiac arrest. Some arrhythmias need no treatment at all. Others require ongoing management.
Medications are often the first approach. For fast heart rates, doctors commonly prescribe drugs that slow the heart’s electrical signals, though these can come with side effects like fatigue, stomach issues, or sleep problems. People with AFib are frequently prescribed blood-thinning medication to reduce the risk of clots and stroke.
Cardioversion uses controlled electrical shocks delivered through pads on the chest to reset the heart’s rhythm. When done in an emergency for ventricular fibrillation, this is called defibrillation. It can also be scheduled as a planned procedure for AFib. Because cardioversion carries a small risk of dislodging blood clots, patients typically take blood-thinning medication before and after.
Catheter ablation is a more targeted procedure for arrhythmias that don’t respond well to medication or keep coming back. A thin, flexible tube is guided through a blood vessel into the heart. The tip of the catheter delivers radiofrequency energy, extreme cold, or laser light to create a small scar on the specific patch of tissue sending out abnormal signals. That scar blocks the faulty electrical pathway. The procedure is done through a blood vessel rather than open surgery, and many people go home the same day or the next.
For persistent slow heart rhythms, an implanted pacemaker can take over the job of the SA node, delivering electrical pulses to keep the heart beating at a steady rate. For people at risk of sudden cardiac arrest from ventricular arrhythmias, an implantable defibrillator continuously monitors the rhythm and delivers a shock if it detects a dangerous pattern.