An irregular heartbeat, called an arrhythmia, happens when the heart’s electrical system misfires or when structural damage interferes with normal signal flow. The causes range from everyday triggers like stress and poor sleep to serious conditions like heart disease and thyroid disorders. Around 52.5 million people worldwide live with atrial fibrillation alone, the most common type of sustained irregular rhythm, and that number has more than doubled since 1990.
How Your Heart Keeps Rhythm
Your heart has a built-in pacemaker: a small cluster of specialized cells in the upper right chamber called the sinus node. This node fires an electrical signal 60 to 100 times per minute under normal conditions. That signal travels to a relay station between the upper and lower chambers, where it pauses briefly before continuing down into the ventricles, causing them to contract and pump blood. An irregular heartbeat occurs when something disrupts any part of this pathway, whether the signal originates too fast, too slow, from the wrong location, or gets blocked along the way.
Heart Disease and Structural Problems
The most common serious causes of arrhythmia involve the heart itself. Coronary artery disease, where narrowed arteries reduce blood flow to the heart muscle, changes electrical signaling in the affected tissue. If a heart attack has already occurred, the resulting scar tissue can block or redirect electrical impulses, creating chaotic rhythms that persist long after the initial event.
Cardiomyopathy, a disease that causes the walls of the heart chambers to stretch, thicken, or stiffen, also sets the stage for rhythm problems. The distorted tissue can’t conduct signals the way healthy muscle does. Heart valve disease creates similar issues: when valves don’t open or close properly, chambers may enlarge over time to compensate, and that physical stretching disrupts the electrical pathways running through the muscle.
Thyroid Disorders
Your thyroid gland has an outsized effect on heart rhythm because its hormones directly influence how fast and how forcefully the heart contracts. An overactive thyroid (hyperthyroidism) raises resting heart rate, increases the force of each beat, and can push cardiac output up by 50 to 300% compared to normal. The most common rhythm disturbance in hyperthyroidism is a persistently fast heartbeat, but atrial fibrillation affects between 2 and 20% of these patients, giving them roughly six times the risk of someone with normal thyroid function.
An underactive thyroid (hypothyroidism) works in the opposite direction, slowing the heart rate and reducing the strength of contractions. While that sounds less dangerous, hypothyroidism can cause serious electrical conduction problems, including a prolonged interval between heartbeats that occasionally triggers life-threatening rapid rhythms in the lower chambers. If you’ve been diagnosed with an irregular heartbeat and no one has checked your thyroid, it’s worth asking about.
Electrolyte Imbalances
The electrical signals in your heart depend on minerals like potassium, magnesium, and calcium moving in and out of cells in precise concentrations. When those levels drop, the system becomes unstable. Low potassium is one of the most well-documented triggers. Patients with potassium levels around 3 mEq/L (normal is 3.5 to 5) can develop premature beats and more complex rhythm disturbances. Low magnesium causes similar problems and is known to trigger both upper and lower chamber arrhythmias.
These imbalances don’t require a dramatic medical event. Heavy sweating, chronic diarrhea, certain blood pressure medications, and even prolonged poor diet can deplete your electrolytes enough to cause skipped beats or palpitations. People who notice irregular heartbeats during or after intense exercise, illness, or periods of inadequate nutrition may be experiencing electrolyte-related rhythm changes.
Stress and the Nervous System
Stress triggers arrhythmias through the autonomic nervous system, the same network that controls your fight-or-flight response. When you experience anxiety, anger, or fear, your body releases adrenaline and related hormones while simultaneously pulling back on the calming signals that keep your heart rate steady. This dual disruption changes the electrical properties of the heart’s upper chambers, shortening the recovery period between beats and creating conditions where signals can loop and misfire.
The effect isn’t limited to one pathway. Both the “accelerator” and “brake” branches of the nervous system can independently provoke irregular rhythms, and they often act together. This is why arrhythmias can occur during moments of acute panic but also during the relaxation period that follows intense stress, when the calming branch rebounds strongly.
Caffeine, Alcohol, and Stimulants
Caffeine and alcohol are two of the most commonly reported triggers for palpitations, though their individual effects are more nuanced than most people assume. In animal studies, neither caffeine alone nor alcohol alone triggered dangerous rhythms at moderate doses. But when combined, the two substances induced rapid, dangerous heart rhythms in every single animal tested. The mechanism involves calcium handling inside heart cells: alcohol increases calcium leakage, while caffeine lowers the threshold at which calcium triggers an extra beat. Together, they overwhelm the cell’s ability to maintain a stable rhythm.
The exact human doses that replicate this effect aren’t established, so blanket recommendations are difficult. But the interaction helps explain why someone might tolerate coffee or wine separately yet experience noticeable palpitations when having both in the same evening. Other stimulants, including nicotine and recreational drugs like cocaine, raise arrhythmia risk through similar stress on the heart’s electrical cells.
Sleep Apnea
Obstructive sleep apnea, where breathing repeatedly stops and starts during sleep, is an underrecognized driver of irregular heartbeats. Each breathing pause drops oxygen levels and jolts the nervous system, creating repeated surges of adrenaline throughout the night. Over time, this takes a measurable toll. One study found that people with sleep apnea had significantly elevated odds of paroxysmal atrial fibrillation, with an adjusted odds ratio of 6.44 compared to people without the condition.
The risks extend beyond atrial fibrillation. Sleep apnea patients face roughly double the odds of general arrhythmias and conduction disorders, and dramatically higher odds of the most dangerous rhythm disturbances. Many people with unexplained palpitations or irregular rhythms, particularly those who snore, wake feeling unrested, or have been told they stop breathing at night, have sleep apnea contributing to the problem.
Medications That Affect Heart Rhythm
Several common classes of medications can alter the heart’s electrical timing, sometimes dangerously. The most potent offenders are certain heart rhythm drugs themselves, which is an ironic but well-known risk. Beyond cardiac medications, the list includes some antibiotics (particularly macrolide and fluoroquinolone types), certain antidepressants (both older tricyclics and some newer SSRIs), antipsychotic medications, and anti-nausea drugs. These medications can delay the heart’s electrical recovery phase, creating a window where abnormal, rapid rhythms can take hold.
The risk is highest when multiple QT-prolonging drugs are taken together, or when they’re combined with low potassium or magnesium levels. If you take any of these medication types and notice new palpitations, fluttering, or dizziness, that’s information worth bringing to your prescriber promptly.
Age as a Risk Factor
Age is one of the strongest predictors of irregular heartbeat, particularly atrial fibrillation. The prevalence of atrial fibrillation is about 2.3% in people over 40, rising to 5.9% in those over 65. Roughly 70% of all people with atrial fibrillation are between 65 and 85 years old. This increase reflects decades of cumulative wear: gradual fibrosis of the heart’s electrical tissue, stiffening of the chambers, and the accumulation of other risk factors like high blood pressure and valve changes. North America has the highest regional incidence, at about 88 new cases per 100,000 people annually.
How Irregular Heartbeats Are Detected
Because many arrhythmias come and go unpredictably, catching one on a recording can be the biggest diagnostic challenge. A standard electrocardiogram captures only about 10 seconds of your heart’s activity, which is useful if the rhythm is abnormal at that moment but misses anything intermittent. For episodes that happen frequently, a 24 to 48 hour ambulatory monitor worn at home is the typical next step.
When symptoms are less frequent, longer monitoring becomes necessary. External loop recorders can track your rhythm for up to 30 days, and they’re well suited for episodes that happen weekly or a few times per month. For the most elusive arrhythmias, with months between episodes, a small implantable recorder placed just under the skin of the chest can continuously monitor for up to three years. The choice of tool depends largely on how often symptoms occur: the rarer the episode, the longer the monitoring window needs to be.