An Irregular Heartbeat Is Called an Arrhythmia: Electrical Signals, Pulse Patterns, and Red-Flag Symptoms

An irregular heartbeat is called an arrhythmia, which means the heart's electrical signaling has slipped out of its normal rhythm. The sinoatrial node, the heart's natural pacemaker, usually fires 60 to 100 times per minute; when that firing becomes too fast, too slow, or chaotic, the result is an arrhythmia. Some forms are harmless, such as occasional premature beats. Others, including atrial fibrillation and ventricular fibrillation, raise stroke or sudden-death risk and need prompt medical care. This guide explains the electrical mechanism, the measurable patterns, the warning signs, and when irregularity becomes an emergency.

How the Heart's Electrical System Produces a Rhythm

Every normal heartbeat begins in a small patch of tissue called the sinoatrial node, sitting in the upper right wall of the right atrium. This node is a cluster of specialized cells that spontaneously depolarize, meaning their internal voltage creeps upward until it crosses a threshold and fires. That self-triggering property is why the heart keeps beating without conscious input.

The sinoatrial node fires, and the electrical wave spreads across both atria, causing them to contract and push blood into the ventricles. The signal then reaches the atrioventricular node, which acts as a deliberate delay gate of roughly 0.1 seconds. That pause lets the ventricles fill before they contract. From there, the signal races down the bundle of His and splits into the left and right bundle branches, then into fine Purkinje fibers that activate the ventricular muscle from the inside out.

At rest, a healthy sinoatrial node discharges about 60 to 100 times per minute. The atrioventricular node, if left to itself, would fire only 40 to 60 times per minute, and the Purkinje fibers just 20 to 40. This hierarchy matters: when the top pacemaker fails, lower backup pacemakers take over at slower rates, which is one reason some arrhythmias produce a sluggish pulse.

An arrhythmia arises from one of two broad faults. Either the impulse is generated abnormally, as when an irritable patch of tissue fires on its own, or the impulse is conducted abnormally, as when a signal gets trapped in a loop and re-enters the same tissue repeatedly. In plain terms: the wiring either sparks where it should not, or the signal takes a wrong turn and keeps circling.

Fast, Slow, and Chaotic: The Main Arrhythmia Types

Arrhythmias are classified by where they start and how they behave. A tachycardia is a heart rate above 100 beats per minute; a bradycardia is below 60. Fibrillation means the muscle quivers without coordinated contraction.

Atrial fibrillation is the most common sustained arrhythmia, affecting an estimated 2 to 6 percent of adults over 65 and rising steeply with age. In atrial fibrillation, the atria fire chaotically at 300 to 600 impulses per minute, and the atrioventricular node lets only some through, so the pulse becomes irregularly irregular. That stuttering atrial flow allows blood to pool in the left atrial appendage, which is why atrial fibrillation multiplies stroke risk roughly fivefold.

Supraventricular tachycardias, including atrioventricular nodal reentrant tachycardia, produce sudden bursts of 150 to 250 beats per minute that start and stop abruptly. Ventricular tachycardia originates in the ventricles and can degenerate into ventricular fibrillation, in which the ventricles quiver uselessly and the heart stops pumping. Ventricular fibrillation is the mechanism behind most sudden cardiac deaths.

Bradyarrhythmias include sick sinus syndrome, where the pacemaker node fires too slowly or pauses, and heart block, where the signal fails to cross from atria to ventricles. Premature atrial and ventricular contractions are single early beats that most people experience and that are usually benign in a structurally normal heart.

This comparison shows why the same word, arrhythmia, covers a harmless skipped beat and a lethal rhythm. The rate, the origin, and the underlying heart structure all change the meaning.

What an Irregular Heartbeat Feels Like: Symptoms and Pulse Patterns

Symptoms track the type and rate of the arrhythmia, not its danger. A person can have atrial fibrillation with no symptoms at all, or feel palpitations from a harmless premature beat. Common sensations include a fluttering or racing feeling in the chest, a sense of a skipped or extra beat, lightheadedness, breathlessness, chest discomfort, and fatigue.

The pulse itself carries diagnostic clues. An irregularly irregular rhythm, where the gap between beats varies with no pattern, points toward atrial fibrillation. A regular rhythm that suddenly jumps to a fast rate and stops just as suddenly suggests a reentrant supraventricular tachycardia. A pulse below 50 beats per minute with dizziness suggests a bradyarrhythmia or heart block.

Syncope, meaning a full faint, is the symptom that most changes urgency. Fainting during exertion or while lying down, as opposed to after standing quickly, raises concern for a dangerous ventricular rhythm. So does a family history of sudden death before age 40, which can signal inherited channel disorders such as long QT syndrome.

Warning Signs That Need Emergency Care

Most arrhythmias are not emergencies, but a specific set of red flags demands immediate action. Call emergency services rather than driving yourself if any of the following occur.

• Fainting or near-fainting, especially during activity or without warning.
• Chest pain or pressure lasting more than a few minutes.
• Severe shortness of breath or difficulty breathing at rest.
• A racing heartbeat that does not slow after several minutes of rest.
• Confusion, cold sweat, or a feeling of impending doom.
• A pulse that is extremely fast, extremely slow, or absent when you feel it.

The threshold to remember is simple: an irregular heartbeat with preserved consciousness and no chest pain can usually wait for an office visit. The same irregularity with fainting, chest pain, or breathlessness is a call for help. Per the 2017 ACC/AHA guidelines, anyone with documented atrial fibrillation should receive a stroke-risk assessment, and that conversation belongs with a clinician, not a search engine.

How Arrhythmias Are Detected: From Pulse to Implantable Monitors

Diagnosis starts with an electrocardiogram, a 10-second recording that captures the heart's electrical trace and costs relatively little. The problem is timing: a paroxysmal arrhythmia that occurs once a week will not appear on a 10-second strip. That is why monitoring escalates in steps.

A Holter monitor records 24 to 48 hours continuously. An event monitor can be worn for 2 to 4 weeks and is triggered when symptoms occur. For infrequent but serious symptoms, an implantable loop recorder, a small device placed under the skin, can monitor the rhythm for up to 3 years. Wearable devices and smartwatch single-lead recordings can flag irregular rhythm but are not diagnostic on their own; they generate suspicion that a clinician must confirm.

Blood tests add context. Thyroid hormone levels matter because an overactive thyroid drives atrial fibrillation, and electrolyte imbalances such as low potassium can provoke premature beats. An echocardiogram checks for structural problems, including valve disease and weakened pumping, that make an arrhythmia more dangerous.

A Corrected Misconception and an Edge Case

The most common misconception is that a "skipped beat" means the heart actually skipped. It usually does not. A premature contraction fires early, and the next normal beat arrives after a compensatory pause, so the extra-long gap feels like a missing beat when the beat was really added. In plain terms: what you feel as a skip is often an extra beat followed by a pause.

A second misconception is that a normal resting pulse rules out arrhythmia. Paroxysmal rhythms can vanish between episodes, and a slow or irregular pulse can be masked by medications such as beta-blockers that hold the rate down. The rhythm, not just the number, is what matters.

An edge case worth knowing is the athlete's heart. Endurance training can slow the resting rate to 40 beats per minute or lower and produce first-degree heart block, both normal adaptations. The same slow rate in an untrained person with dizziness is a different story. Context, not the number alone, decides whether a bradycardia is a problem.

What to Actually Do When You Notice an Irregular Heartbeat

Concrete steps convert worry into useful information. Start by documenting the episode rather than dismissing it, because a pattern of timing is exactly what a clinician needs.

• Note the date, time, duration, and what you were doing when the irregularity began.
• Record your pulse rate and whether the rhythm felt regular or irregular.
• Capture a smartwatch or home monitor tracing if you have one, since it may guide testing.
• Limit caffeine, alcohol, and stimulant cold medicines, which commonly trigger premature beats.
• Keep a list of all medications and supplements, because thyroid pills and decongestants can provoke arrhythmia.
• Schedule a visit if symptoms recur, and treat fainting or chest pain as an emergency.

If you have diagnosed atrial fibrillation, the practical priorities are stroke-risk assessment, rate or rhythm control, and anticoagulation when indicated. Per the 2019 AHA/ACC/HRS atrial fibrillation guideline, anticoagulation decisions rest on validated risk scores rather than on how symptomatic the rhythm feels. That distinction matters because a silent arrhythmia still carries stroke risk.

Limits of What This Explanation Can Tell You

This guide describes mechanisms and typical patterns, but it cannot diagnose an individual heart. The same symptom, a fluttering chest, can reflect anxiety, thyroid disease, a benign premature beat, or atrial fibrillation, and only a recording during the episode can separate them. Rhythm disorders also evolve; an arrhythmia that is benign today can change with age, new medications, or structural heart disease.

The numbers here are population averages, and individual thresholds vary with age, fitness, and medication. A resting rate of 55 beats per minute can be perfectly healthy in a trained runner and concerning in a frail older adult on a rate-slowing drug. In plain terms: use these ranges to recognize what is unusual for you, not to self-diagnose. The single most useful action is to get the rhythm recorded while it is happening, because a documented trace is worth more than any description of a sensation.