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Your heart fires roughly 100,000 times a day, and most of that happens without you noticing a thing. The trouble starts when the electrical signals that set the pace misfire. The result is an arrhythmia, or heart rhythm disorder. Some are harmless hiccups that feel stranger than they are dangerous. Others are emergencies measured in minutes. Learn the difference, and you will know when a flutter in your chest is worth a phone call and when it is worth calling an ambulance.
How the Heart’s Wiring Sets the Rhythm
Each beat starts in a small patch of tissue called the sinus node, high in the right atrium. From there the signal spreads across the atria, pauses briefly at the AV node, then races down pathways into the ventricles, which squeeze and push blood out to the body.
An arrhythmia happens for one of two reasons: a spot in the heart starts firing when it shouldn’t (a rhythm that is too fast or too chaotic), or the signal gets delayed or blocked on its way through (a rhythm that is too slow). Nearly every disorder in the list below fits one of those two patterns.
1. Atrial Fibrillation (AFib)
AFib is the most common sustained arrhythmia, and it is the one most likely to land someone in hospital. Instead of a single clean contraction, the atria quiver with hundreds of chaotic electrical impulses per minute. The ventricles still beat, but irregularly and often fast, so the pulse feels like a bag of worms under the fingers.
This is what makes AFib more than an annoyance. When the atria stop squeezing properly, blood pools in a small pouch called the left atrial appendage and can clot. That clot travels, and the result is a stroke risk roughly five times higher than average, which is why preventing and treating stroke is a core part of managing AFib, alongside blood thinners and rate control.
What AFib typically feels like
- A fluttering or pounding chest, often worse at night or after alcohol
- Unusual tiredness during ordinary activity, like climbing a flight of stairs
- Shortness of breath, dizziness, or an odd sense of doom
- No symptoms at all in maybe a third of cases, found on a routine pulse check
2. Atrial Flutter
Flutter is AFib’s tidier cousin. Rather than chaos, a single electrical circuit loops around the right atrium at about 300 beats a minute. The AV node usually lets every second impulse through, producing a ventricular rate stuck near 150, sometimes with a pulse so regular it feels mechanical.
The practical difference matters: flutter responds well to a procedure called catheter ablation, with success rates above 90 percent for the typical circuit. People can also hold flutter for hours while feeling only mildly off, which is why a heart rate that sits at exactly 150 is worth a second look.
3. Supraventricular Tachycardia (SVT)
SVT is the classic “my heart suddenly took off” story. It starts and stops like a switch. Someone is sitting on the sofa and their pulse jumps from 70 to 190 in a single beat, then reverts just as abruptly twenty minutes later. The most common form, AV nodal reentrant tachycardia, is often seen in healthy young adults, and it is especially common in women in their twenties and thirties.
Emergency doctors often break an SVT episode by having the patient bear down as if straining, or by using a drug called adenosine that briefly stops the heart’s electrical activity. Babies and children can get SVT too, and those born with structural heart problems are at higher risk, which is one reason congenital heart defect treatment and prevention deserves attention from infancy rather than decades later.
4. Premature Beats (PVCs and PACs)
This is the “skipped beat” almost everyone has felt: a strange thud in the throat, then a pause, then a stronger beat. Nothing was actually skipped. An extra beat fired early from somewhere in the atria or ventricles, and what you noticed was the long filling pause that followed.
In a healthy heart, occasional premature beats are normal, and most people have hundreds a day without knowing. Coffee, poor sleep, dehydration and stress all nudge the number up. The picture changes when they become very frequent. When premature ventricular contractions make up more than roughly 10 to 20 percent of all beats, the heart muscle can stretch and weaken over months. That condition, PVC-induced cardiomyopathy, often reverses once the extra beats are controlled, so cardiomyopathy treatment sometimes starts with an electrophysiologist rather than a heart failure clinic.
5. Ventricular Tachycardia (VT)
VT is three or more ventricular beats in a row, running fast. On a monitor it looks like a row of identical wide spikes. A short burst of a few seconds may only cause lightheadedness. A longer run can drop blood pressure fast enough that a person passes out mid-sentence.
The danger level depends almost entirely on the underlying heart. VT in a structurally normal heart is often tolerated. VT in a heart scarred by a previous heart attack is a different animal, and it can deteriorate into the rhythm below. That is the reasoning behind implantable defibrillators, small devices that watch the rhythm continuously and deliver a corrective shock within seconds.
6. Ventricular Fibrillation
VFib is the reason AEDs hang on walls in train stations. The ventricles stop pumping entirely and just quiver, so blood flow to the brain stops within seconds. A person collapses, stops breathing normally, and may make gasping sounds that bystanders mistake for breathing.
Survival hinges on what happens in the first few minutes. CPR keeps oxygen moving, and a defibrillator shock restarts the rhythm. Every minute without a shock drops survival by around 7 to 10 percent. Overall survival after an out-of-hospital cardiac arrest sits near 10 percent in most registries, and immediate bystander CPR can roughly double it. This is a rhythm where the person next to the patient matters more than the hospital.
7. Bradycardia and Heart Block
A resting heart rate under 60 is not automatically a problem. Fit cyclists and distance runners routinely sit in the 40s because their hearts pump more blood per beat. Bradycardia becomes a disorder when the slow rate causes symptoms: fatigue, exercise intolerance, near-fainting, or actual blackouts.
Two patterns show up frequently. Sick sinus syndrome means the natural pacemaker pauses or fires too slowly, often in people over 70. Heart block means the signal is delayed or dropped between the atria and ventricles. First-degree block is usually harmless. Third-degree, or complete, block is not, and it is one of the clearest reasons for a pacemaker.
There is also a rare congenital form, where antibodies from a mother with lupus damage the fetal AV node in the womb. Those babies need pacing early in life, and they are a reminder that arrhythmias are not exclusively an older person’s problem.
Signs You Should Not Sit On
Some symptoms are easy to rationalise away as anxiety or too much coffee. A few are not.
- Fainting, or nearly fainting, especially during exertion or while lying down
- A pulse over 150 that does not settle within a few minutes
- Chest pain or breathlessness alongside a racing or irregular heartbeat
- A resting pulse that stays under 50 with fatigue or dizziness
- A family history of sudden cardiac death before age 50
A single-lead ECG at the clinic takes about the time it takes to remove a jacket, but arrhythmias are notorious for hiding during a ten-second recording. If symptoms come and go, a 24 or 48 hour Holter monitor, a two-week event patch, or a small implantable loop recorder under the skin will catch far more than a rushed office visit.
What Changes After a Diagnosis
Most people walk out of an electrophysiology clinic with a plan rather than a sentence. Catheter ablation, where a thin wire is threaded through a vein in the groin to burn or freeze the misbehaving tissue, now cures many SVTs and flutters outright and controls a growing share of AFib cases. Medications remain useful for rate control and stroke prevention. Devices fill the gap when neither works.
The lifestyle levers are less glamorous but rarely wasted. Untreated sleep apnoea is one of the strongest triggers for AFib recurrence, and treating it can cut the number of episodes. Alcohol, even a couple of drinks at the weekend, raises the odds of an AFib attack within hours. Losing 10 percent of body weight has been shown to reduce AFib burden measurably in people who are overweight.
Meanwhile, the technology that watches for these rhythms has quietly moved onto our wrists. A smartwatch will not diagnose you, and it will generate plenty of false alarms in people with perfectly normal hearts. It will, however, occasionally pick up silent AFib in someone who felt fine, and that early flag is often the difference between a treatable condition and a stroke.
