Orthostatic tachycardia (HR rise on standing)

Start here: a 30-beat jump on standing

Gravity pulls roughly a soda can's worth of blood down into your legs and belly every time you stand. A healthy body clamps those vessels and keeps the brain supplied without you noticing. In POTS that reflex underperforms, less blood returns to the heart, and the body's backup plan is to flood the system with adrenaline and crank the heart rate up to keep flow going.

So the racing heart is a symptom of the fix, not the original fault. The diagnostic threshold is a rise of at least 30 beats per minute, or 40 in teenagers, within ten minutes of standing, with symptoms and without a big blood-pressure drop. Patients describe palpitations, lightheadedness, shakiness, and a brain that fogs over the longer they stay upright.

How it is confirmed

Confirming POTS does not require fancy equipment. A clinician measures your heart rate and blood pressure lying down, then has you stand or lean against a wall for up to ten minutes while recording the change. This active stand test, sometimes called a NASA lean test, is the standard and well-founded way to capture the rise.

The test matters because the diagnosis is defined by numbers, not by how dramatic the symptoms feel. A clean record of the heart-rate climb, without a matching blood-pressure fall, separates POTS from simple low blood pressure and from anxiety, and it gives you something objective to bring to an appointment when symptoms are easy to dismiss.

standard testwell-founded

Too little blood to work with

One consistent finding is that many people with POTS run on less circulating blood than they should. Careful measurements of blood volume have repeatedly shown a deficit, which means there is simply less fluid in the tank to push toward the brain when you stand.¹

A more recent and precise method, rebreathing a trace gas to gauge volume, confirmed the same shortfall.² This is encouraging in a practical way, because volume is something you can act on. Adding salt and fluids, and using compression to stop blood from pooling, all aim straight at this deficit. The grade of evidence here is modest and partly borrowed from general POTS research, so it guides management rather than settling the cause.

low to thin gradepartly borrowed from general POTS data

Nerves that lost the thread

A second mechanism is damage to the small nerve fibers that tell blood vessels when to tighten. If those signals weaken, the vessels in your legs fail to clamp on cue, blood pools, and the heart races to compensate. Examinations of nerve tissue, including the vagus nerve, have found viral genetic material and inflammation in this setting.

This route, autonomic and small-fiber nerve injury, has reasonable support, though the studies are small. It fits a wider pattern in which the long COVID problem is not the heart or vessels themselves but the nervous wiring that is supposed to control them.

low to moderatewell-founded routesmall sample sizes

Autoantibodies: a contested lead

A more debated idea is that antibodies bind the receptors that govern the standing reflex, the adrenergic and muscarinic receptors, and distort the signal. If real, this would tie POTS directly to the autoimmune mechanism seen elsewhere in long COVID.

The reason to hold this loosely is that the same antibodies turn up in plenty of healthy people, so their presence does not prove they are causing the tachycardia. This is a genuine association under active study, not a confirmed cause, and it should be described that way.

low to moderateantibodies also in healthy controlsassociation not causation

Mast cells and serotonin

Two further leads round out the picture. In a subset of people, mast cells, the immune cells behind allergic reactions, appear overactive and release chemicals that can drive tachycardia and flushing. This subset sometimes responds to antihistamines, though the evidence is still emerging.

Separately, a small cohort linked POTS to a platelet storage problem and low serotonin, and serotonin reduction has been reported more broadly after viral infection.³⁴ These are thin, single-study leads. They are worth knowing because they hint at treatable subgroups, but they are not yet a basis for routine treatment.

thinpossible treatable subgroups

What helps: slow the heart, fill the tank

Treatment works on two fronts. Filling the tank comes first and needs no prescription: more salt and fluid, compression garments over the legs and belly, sleeping with the head slightly raised, and rebuilding fitness with recumbent exercise like a rowing machine or recumbent bike that does not force you upright. A systematic review of POTS after COVID supports this layered approach.⁵

Slowing the heart is the second front. A drug that lowers heart rate without dropping blood pressure has the strongest trial evidence in this setting, with a controlled study showing a meaningful reduction in the standing heart-rate climb. Beta-blockers are also used, with weaker and mostly borrowed data, and a volume-retaining steroid has Cochrane-reviewed evidence for orthostatic symptoms.⁶ No treatment is approved specifically for long COVID POTS, so all of this is off-label and belongs under medical supervision.

heart-rate drug: controlled-trial supportbeta-blockers: weaker, borrowed datasalt, fluids, compression: first-line

What this means for you

If your heart races whenever you stand and steadies when you lie down, ask for a simple stand test rather than accepting that it is anxiety. The diagnosis rests on a measured heart-rate rise, and having that number changes the conversation. POTS after COVID is common and recognized, and the racing heart is your body overcompensating for poor blood return, not a sign your heart is failing.

Most of the first-line help needs no prescription and is worth starting while you wait for specialist care: more salt and fluids unless a doctor has told you otherwise, compression garments, and gentle recumbent exercise that does not force you upright. If those are not enough, a heart-rate-slowing drug has the best trial evidence, but every medication option here is off-label and can affect blood pressure, so it needs a clinician. Pair any plan with pacing, because standing tachycardia and post-exertional crashes often travel together.

References

Each reference links to the source on PubMed, PMC, or the publisher.

1. Blood volume perturbations in the postural tachycardia syndrome. American Journal of the Medical Sciences, 2007.
2. Blood volume deficit in POTS assessed by a semiautomated carbon monoxide rebreathing method. 2025.
3. Postural orthostatic tachycardia syndrome is associated with platelet storage pool deficiency. Medicine, 2017.
4. Serotonin reduction in post-acute sequelae of viral infection. Cell, 2023.
5. Postural orthostatic tachycardia syndrome after COVID-19: a systematic review of therapeutics. 2023.
6. Fludrocortisone for orthostatic intolerance (Cochrane review). 2021.