Your Heart Skips a Beat

TL;DR: That feeling where your heart seems to pause for a second and then thump is almost always an extra beat that came too early. The early beat is too small to feel, the pause after it gives your heart extra time to fill, and the next beat hits harder than usual. That hard beat is the one you feel. In a normal heart this is common and not dangerous, but it is annoying, and there is usually a reason for it that we can find. The usual causes are low magnesium, low potassium, thyroid trouble, low iron, caffeine, alcohol, nicotine, not enough water, and not enough sleep. Magnesium glycinate in the evening helps a lot of people. Get checked sooner if you faint or nearly faint, if it gets worse when you exercise rather than better, or if someone in your family died suddenly and young.

Why does a skipped beat feel like a pause and then a thump?

Because that is close to what is happening, and understanding it takes most of the fear out of it.

Your heart normally beats on a signal that starts in one place and travels in order. Sometimes a different patch of heart muscle fires early on its own. If that patch is in the lower chambers, it is a premature ventricular contraction, a PVC. If it is in the upper chambers, it is a premature atrial contraction, a PAC.

The early beat happens before the heart has finished filling, so it moves very little blood and you generally do not feel it. What follows is a slightly longer pause while the rhythm resets, and during that pause the heart fills more than it usually would. The next beat then ejects a larger volume with more force. That beat is the thump.

So the sensation people describe as a skip is a pause plus a strong beat, and the missing beat was there the whole time, just too small to notice. People often find it more alarming lying down at night, when there is nothing else competing for attention and the chest is against the mattress.

Are they dangerous?

In a structurally normal heart, occasional premature beats are not dangerous, and they are extremely common. Recordings of healthy people without symptoms find them routinely.

That is a genuine reassurance and it is also where a lot of patients get stranded. Being told something is benign frequently gets heard as being told to stop mentioning it, and the symptom keeps happening. Benign and worth addressing are not in conflict. Most of these have drivers underneath, the drivers are modifiable, and correcting them usually reduces both the frequency and the awareness.

There are 2 situations where the picture changes. The first is a structurally abnormal heart, meaning prior heart attack, cardiomyopathy, significant valve disease, or heart failure, where premature beats carry more weight and belong in a cardiologist's hands. The second is a very high burden. When PVCs make up a large share of total beats, commonly cited above 10 to 15% on a 24-hour monitor, they can weaken the heart muscle over time, a reversible condition called PVC-induced cardiomyopathy. That is the specific reason we quantify the burden rather than only confirming the beats exist.

What drives them?

A short list covers most of what we find, and it is worth going through deliberately rather than guessing.

Magnesium is the one that most often moves the needle, and serum magnesium is a poor way to check it, because the body defends the blood level while tissue stores fall. An RBC magnesium reflects what is inside cells, and we aim for the upper part of that range rather than the bottom. Magnesium glycinate is the form we use here, since it absorbs well and does not loosen stools the way oxide does, and taking it in the evening suits both the rhythm and the sleep.

Potassium matters for the same electrical reasons and is worth checking alongside, particularly in anyone on a diuretic.

Thyroid. An overactive thyroid raises the frequency of premature beats and the awareness of them. A TSH belongs in this workup every time.

Iron. Low iron and anemia make the heart work harder and make palpitations more noticeable, and in menstruating women this is a common and correctable finding. Ferritin rather than hemoglobin alone.

Stimulants and the obvious suspects. Caffeine, alcohol, nicotine, cannabis, decongestants such as pseudoephedrine, and prescription stimulants all provoke them. Alcohol is the one people are most surprised by, and the effect frequently shows up the following day rather than the same evening.

Sleep and stress. Short sleep, untreated sleep apnea, and periods of high adrenaline all increase both the beats themselves and how much you notice them. Apnea deserves particular attention when the beats cluster overnight, and a home sleep test is an inexpensive way to answer it.

Dehydration, which is easy to correct and easy to miss in people who train.

What does the workup look like?

Proportionate to the symptom, and it does not need to be elaborate.

An ECG in the office documents the beats when they are frequent and screens for the conduction abnormalities that would change the plan. A monitor worn at home, for 24 or 48 hours or for a couple of weeks depending on how often the symptom occurs, is what establishes the burden and correlates the beats with what you were feeling at the time. That correlation is worth more than most people expect, since it can confirm the alarming sensation and the recorded beat are the same event.

Labs cover magnesium, potassium, TSH, and iron studies with ferritin, along with a metabolic panel.

An echocardiogram enters the picture when the burden is high, when the exam or ECG raises a question, or when there is a family or personal history that warrants looking at the structure directly.

What helps?

Correct the drivers first, because that is where most of the benefit lives and none of it requires a prescription.

Fill the magnesium gap, treat the iron if it is low, settle the thyroid if it is off. Pull back caffeine and alcohol for a defined stretch rather than permanently, long enough to see whether it changes anything, since 2 weeks of honest reduction answers the question better than an argument about it. Protect sleep, and test for apnea when the pattern fits.

When the beats remain frequent and bothersome after that, a beta blocker is the usual next step. It does not eliminate the premature beats so much as blunt the forceful beat that follows, which is the part you feel, and it lowers the adrenaline drive that provokes them. Which form of metoprolol you take matters more than most people are told.

For a small group with a high burden that has not responded, catheter ablation targets the specific spot generating the beats and is highly effective, and that conversation belongs with an electrophysiologist.

When should I be seen sooner?

Some features move this from a nuisance to something that gets evaluated promptly.

Fainting or nearly fainting with the palpitations. Palpitations that get worse with exertion rather than settling. Chest pain or breathlessness alongside them. A family history of sudden cardiac death or of an inherited heart condition. Known structural heart disease. A sustained fast rhythm rather than isolated beats, particularly if it starts and stops abruptly.

Any of those deserves a same-week evaluation rather than a note at your next physical. Chest pain with a fast rhythm, or fainting, is an emergency department visit rather than a message.

Guidance from the Clinic

"Being told a symptom is benign and being told it does not matter are 2 different messages, and patients almost always hear the second one. Skipped beats in a normal heart will not hurt you, and they still ruin your evening, and there is nearly always something underneath worth correcting. I check the magnesium properly, the thyroid, and the iron before anyone concludes they simply have to live with it, because that list explains most of what walks through the door."

Related at Fishtown Medicine

• Metoprolol: Tartrate vs Succinate - which form, and the pill-in-the-pocket approach
• Magnesium Glycinate Clinical Guide - the RBC target and why the form matters
• Racing Heart When Standing (POTS) - when the pattern is positional
• Home Sleep Apnea Testing - when the beats cluster overnight
• Understanding High Blood Pressure at Home - measuring properly at home

Scientific References

1. Ng GA. "Treating patients with ventricular ectopic beats." Heart. 2006;92(11):1707-1712. PubMed
2. Baman TS, Lange DC, Ilg KJ, et al. "Relationship between burden of premature ventricular complexes and left ventricular function." Heart Rhythm. 2010;7(7):865-869. PubMed
3. Marcus GM. "Evaluation and Management of Premature Ventricular Complexes." Circulation. 2020;141(17):1404-1418. PubMed
4. Workinger JL, Doyle RP, Bortz J. "Challenges in the Diagnosis of Magnesium Status." Nutrients. 2018;10(9):1202. PubMed