Most palpitations have an everyday explanation. Caffeine, short sleep, stress, alcohol, hard training and some medications are the usual triggers, and life stages such as pregnancy and perimenopause add their own. Blood tests can explain part of the rest, mainly thyroid function, hemoglobin, potassium and magnesium. A clinician interprets results in context.
Everyday triggers account for most palpitations, not a disease. Caffeine, nicotine, alcohol, short or broken sleep, stress and anxiety, dehydration, a heavy training block, large meals and several common medications explain a large share of what people feel.
A palpitation is the awareness of your own heartbeat, felt as a thud, a flutter, a skipped beat or a run of fast beats. The most common pattern is a single early beat followed by a pause, after which the next beat lands harder because the heart has had slightly longer to fill. That stronger beat is usually what gets noticed, not the skip itself.
Studies indicate that palpitations presenting in general practice most often trace back to a rhythm disturbance, to anxiety or panic, or to no cause that is ever identified 1. Reviews of the symptom describe the same short list of everyday contributors alongside the cardiac ones 2.
Stimulants are the obvious first suspect. Coffee, energy drinks, strong tea, nicotine and pre-workout formulas all raise adrenergic drive, and sensitivity varies a lot between people. Two coffees that one person never notices can produce an afternoon of fluttering in someone else. Alcohol belongs in the same group, including the night after drinking, when sleep is fragmented and the heart rate runs higher than usual.
Sleep and stress work through the same pathway. A short night, a jet-lagged week or a stretch of high workload keeps the sympathetic nervous system busier than normal, and a busier nervous system produces more ectopic beats and more awareness of ordinary ones. Palpitations noticed lying in bed are extremely common, partly because the room is quiet and the chest is pressed against the mattress, which makes the beat easier to feel.
Training load matters too. Hard sessions, poor hydration and salt loss from sweating all change the conditions the heart works in. In athletes, research suggests that most palpitations turn out to be benign, though symptoms that appear during exertion deserve a careful workup rather than reassurance 3.
Several widely used medicines can speed the heart or make beats feel stronger. Decongestants, inhaled asthma relievers, thyroid hormone replacement, some antidepressants, some stimulant medicines for attention disorders and some over-the-counter supplements are frequent contributors, which is why published approaches to palpitations include a full medication and supplement review 4. Do not stop a prescribed medicine on your own. A licensed provider evaluates whether a medication is contributing and whether any change is appropriate.
Life stage shifts the picture as well. Pregnancy raises blood volume and resting heart rate, and palpitations are a common complaint during it. Perimenopause brings fluctuating hormones, broken sleep and hot flushes, each of which can make the heartbeat more noticeable. In older adults, reviews of urgent palpitations note that a rhythm cause becomes more likely with age and is worth evaluating properly rather than brushing off 5.
None of this is a diagnosis. It is a list of things worth looking at before anyone reaches for a lab slip, and for many people the pattern resolves once two or three of them are fixed.
A short blood panel covers the measurable metabolic causes, which means thyroid function through TSH and Free T4, hemoglobin for anemia, and potassium and magnesium for the electrolytes that shape heart rhythm. Blood work does not replace a rhythm recording, and primary care recommendations pair history, examination and an ECG with targeted blood tests rather than relying on labs alone 6.
| Marker | Why it is linked to this symptom | What a result can and cannot tell you |
|---|---|---|
| TSH | The pituitary signal that rises when thyroid output is low and falls when it is high, so a low TSH points toward an overactive thyroid, which speeds the heart. | A low or high TSH flags a thyroid axis worth investigating further. It cannot confirm a rhythm problem, and a single value can be shifted by illness, pregnancy or medication. |
| Free T4 | The circulating thyroid hormone available to tissues, including heart muscle, where excess raises rate and contractility. | Read with TSH, it shows how much hormone is actually circulating. On its own it cannot separate a thyroid cause from a stimulant or anxiety cause. |
| Hemoglobin | Carries oxygen. When it is low, the heart compensates with a faster, stronger beat, which is often felt as pounding. | It identifies anemia and its severity. It does not show why hemoglobin is low, so iron studies or other tests usually follow. |
| Potassium | Sets the resting electrical state of heart muscle cells, so values above or below the usual range can alter rhythm. | A result outside the typical range is worth discussing with a clinician promptly. A normal value does not rule out an arrhythmia, and poor sample handling can falsely raise the number. |
| Magnesium | Influences cardiac conduction and the body's handling of potassium, and low levels are listed among metabolic contributors to ectopic beats. | A low serum value supports the case for depletion. A normal serum value does not exclude it, because most body magnesium sits inside cells and bone. |
Typical lab reference ranges for these markers look roughly like the table below.
| Marker | Typical lab reference range |
|---|---|
| TSH | 0.4 to 4.0 mIU/L |
| Free T4 | 0.8 to 1.8 ng/dL |
| Hemoglobin | 13.5 to 17.5 g/dL (men), 12.0 to 15.5 g/dL (women) |
| Potassium | 3.5 to 5.1 mmol/L |
| Magnesium | 1.7 to 2.2 mg/dL |
These are typical lab reference ranges, not targets. Ranges vary by lab, age and sex, so always read your number against the range printed on your own report.
Yes, an overactive thyroid is one of the classic reasons for a fast or forceful heartbeat, and TSH is usually the first test ordered to look for it. Thyroid hormone increases how strongly heart muscle responds to adrenaline, which raises resting heart rate, shortens the time between beats and makes each contraction more forceful. Clinical approaches to palpitations include thyroid function among the baseline blood tests for exactly this reason 7.
TSH works backwards from what most people expect. The pituitary releases less TSH when there is plenty of thyroid hormone circulating, so a low TSH is the signal that points toward overactivity, and a high TSH points the other way. An underactive thyroid can also produce palpitations indirectly, usually through fatigue, deconditioning and poor sleep rather than through a fast rate.
Plenty of things besides thyroid disease move TSH. Acute illness, recent surgery, pregnancy, time of day, steroid medicines, high-dose biotin supplements that interfere with some assays and the dose of any thyroid medication a provider has prescribed can all shift the number. A single out-of-range TSH is an observation, not a conclusion.
The practical next step is simple. An out-of-range TSH usually gets repeated with Free T4, and sometimes with thyroid antibodies, before anyone draws a conclusion. A licensed provider decides whether any treatment is appropriate and what further testing makes sense.
Free T4 is checked alongside TSH because it measures the thyroid hormone actually circulating and available to tissues, including heart muscle. Free T4 is the unbound fraction, the part not stuck to carrier proteins, which is what makes it a better reflection of hormone activity than a total hormone measurement.
TSH and Free T4 answer different questions. TSH tells you what the pituitary thinks about thyroid supply. Free T4 tells you what the supply is. The two usually agree, and when they do not, the mismatch itself is informative. Early or mild overactivity can show a suppressed TSH while Free T4 still sits inside the typical range. Non-thyroidal illness, some medications and rare pituitary problems can also push the pair out of step, which is why thyroid tests are read as a set rather than one number at a time.
Free T4 moves for non-thyroid reasons too. Fasting status and the time between a thyroid medication dose and the blood draw also matter.
If both TSH and Free T4 sit comfortably inside the typical range, the thyroid is an unlikely explanation for the symptom and attention usually moves to rhythm recording, sleep, stimulants and the other markers on this page.
Yes, low hemoglobin is a well-recognised reason for a pounding or racing heartbeat, because less oxygen carried per beat means the heart has to move more blood to deliver the same oxygen. Hemoglobin is the protein inside red blood cells that does the carrying, and it is measured as part of a complete blood count.
The pattern is usually more than palpitations alone. Breathlessness on stairs, unusual fatigue, pale skin, cold hands, headaches and dizziness on standing often travel with it. In people with cancer, reviews of palpitations specifically list anemia alongside electrolyte shifts and drug effects as reversible contributors worth checking before anything else is assumed 8.
A hemoglobin result tells you how much oxygen-carrying capacity is present, not why. Heavy menstrual bleeding, low iron intake, poor iron absorption, slow gastrointestinal blood loss, B12 or folate shortfall, kidney disease and chronic inflammation all reduce it through different routes, so iron studies, ferritin and a look at red cell size usually follow a low result. Hydration also matters, since a dehydrated sample can read falsely high and a very well hydrated one falsely low. Altitude, smoking and pregnancy all shift the expected value too.
A low hemoglobin is worth discussing with a clinician, because the useful question is what is causing it rather than how to push the number back up.
Yes, potassium is central to the electrical behaviour of heart muscle, which is why it appears on almost every palpitations workup. Potassium sets the resting membrane potential of cardiac cells, and both low and high values change how easily those cells fire and reset, which can show up as extra beats or a rhythm that feels irregular.
In the standard approach to the symptom, electrolyte disturbance is associated with rhythm problems clearly enough that a basic metabolic panel is ordered early 6. Higher values more often relate to kidney function, dehydration or specific medication classes that reduce potassium excretion.
One quirk is worth knowing. Potassium leaks out of red cells after a blood draw, so a tight tourniquet, a clenched fist during sampling, a difficult draw or a delay before processing can all produce a falsely high reading. A surprising high result is often repeated with careful technique before anyone acts on it.
A potassium value outside the typical range is suboptimal and worth discussing with a clinician promptly, especially alongside palpitations, muscle cramps or weakness. Never try to correct it yourself with supplements or salt substitutes, because the direction of the problem is not something you can feel.
Magnesium acts as a cofactor in the pumps that move potassium and calcium across heart cell membranes, so when magnesium runs low, potassium handling suffers too, and the two deficits often appear together.
Magnesium gets depleted by routes most people recognise. Heavy sweating over a long training block contributes as well, which is one reason the marker comes up often in endurance athletes.
The interpretation needs honesty about what serum magnesium measures. Only a small fraction of total body magnesium circulates in blood, with most of it inside cells and bone, so a result inside the typical range does not rule out depletion, while a result below the range makes depletion quite likely. That asymmetry is why the value is read alongside potassium, calcium, symptoms and medication history rather than on its own.
If the number is low, the next step is finding the drain rather than guessing at replacement. A licensed provider evaluates whether any supplementation or further testing is appropriate for your situation.
A completely normal blood panel does not rule out a rhythm problem, because blood tests do not record the heartbeat. The only way to know what the heart was doing during a palpitation is to capture it electrically, which is why evaluation centres on an ECG and, when symptoms are intermittent, on longer monitoring with a Holter, an event recorder, a patch monitor or in some cases a consumer wearable 2.
Several causes sit outside what any panel shows. Structural issues such as valve problems or thickened heart muscle need imaging rather than bloods. Atrial fibrillation, supraventricular tachycardia and frequent ectopic beats are electrical findings. Panic disorder and generalised anxiety produce genuine, strongly felt palpitations with entirely normal labs. Obstructive sleep apnoea, postural orthostatic tachycardia and the aftermath of a viral illness all belong on the list too. Older reviews of the symptom make the same point, that a careful history of how the beat starts, how it stops and what it feels like often narrows the cause more than any single test does 9.
The useful way to hold this is that blood markers rule in or rule out a specific set of explanations. They are quick, cheap and worth doing, and they are one input among several rather than the answer.
Some patterns need urgent assessment rather than watchful waiting. Call 911 or your local emergency number if palpitations come with chest pain or pressure, fainting, severe shortness of breath, confusion, or a fast heartbeat that will not settle.
Seek prompt medical care, within days rather than months, in these situations.
Anxiety and panic deserve the same seriousness as any other cause, because the symptom is real and the distress is real. If you are having thoughts of self-harm, call or text 988 (US) or your local emergency number now.
Do not try to diagnose yourself from a number or a wearable alert. Bring the recording, the pattern and your medication list to a clinician and let them interpret it.
All five markers on this page sit in one routine blood draw. The FitScript Essential panel measures TSH, Free T4, hemoglobin, potassium and magnesium together, so thyroid function, anemia and the two rhythm-relevant electrolytes can be read side by side rather than chased one test at a time.
Results only help if they are understood. Atlas, FitScript's AI health advisor, explains each marker in plain language, shows how values relate to one another and flags what is worth raising with a clinician. The membership includes 150+ biomarkers tested per year, so changes over time are visible rather than guessed at. A licensed clinician reviews findings and decides on any treatment, and nothing on a results page substitutes for that review.
This page is educational and is not medical advice. Discuss your results, and any treatment, with a clinician or licensed provider before acting on them.
Everyday triggers cause most palpitations, including caffeine, nicotine, alcohol, short sleep, stress, dehydration and hard training. Medications such as decongestants and inhaled asthma relievers contribute, as do pregnancy and perimenopause. Measurable causes include thyroid overactivity, anemia and low potassium or magnesium, which a clinician interprets alongside an ECG.
Heart palpitations are the awareness of your own heartbeat, felt as a thud, flutter, skipped beat or run of fast beats. The most common pattern is an early beat followed by a pause, so the next beat feels stronger. Episodes with chest pain or fainting need emergency care immediately.
Causes fall into three groups. Lifestyle triggers come first, such as stimulants, alcohol, poor sleep, stress and dehydration. Metabolic causes come second, including an overactive thyroid, anemia and electrolyte shifts. Cardiac rhythm causes come third and need an ECG or a monitor, because no blood test records the heartbeat.
Yes, dehydration is one possible reason. Lower circulating volume means the heart beats faster to maintain output, and fluid loss through sweating, vomiting or diarrhoea also shifts potassium and magnesium, both of which influence rhythm. Palpitations that appear after heavy sweating or illness are worth mentioning to a clinician.
Low iron can contribute when it has reduced hemoglobin, since less oxygen carried per beat makes the heart work harder and beat more forcefully. Fatigue, breathlessness on stairs and pale skin often appear alongside. A blood count plus iron studies shows whether this is part of the picture.
Lying still in a quiet room makes ordinary heartbeats far easier to feel, and lying on the left side presses the heart closer to the chest wall. Late caffeine, alcohol, a large evening meal and a stressful day all add extra beats. Persistent night-time episodes still deserve assessment.
Yes, anxiety and panic produce genuinely felt palpitations with completely normal blood work, because adrenaline raises heart rate and makes each beat stronger. The symptom is real, not imagined. A clinician usually rules out thyroid, anemia and rhythm causes first, since the explanations can overlap in the same person.
The common ones are TSH and Free T4 for thyroid function, hemoglobin from a complete blood count for anemia, and potassium and magnesium for electrolytes. These cover the measurable metabolic causes. They do not record rhythm, so an ECG or longer monitoring is usually arranged alongside them.