Rapid Heartbeat: Causes and When to Worry

What counts as a rapid heartbeat

A normal resting heart rate for adults is 60 to 100 beats per minute (bpm). Fit athletes may sit in the 40s or 50s. Above 100 bpm at rest is tachycardia. Children have higher normal rates: babies 100 to 160 bpm, and young children 80 to 130 bpm.

To check your pulse, rest for 5 minutes, place two fingers on the thumb side of your wrist or the side of your neck, and count for 30 seconds then double it. Note whether the rhythm is regular or irregular. Smartwatches give a good estimate and some can record an ECG.

A rapid heartbeat is not always felt. When you do notice it, as pounding, fluttering or racing, it is called palpitations.

Normal and everyday causes

These raise the heart rate through normal adrenaline-driven sinus tachycardia, where the heart's natural pacemaker simply speeds up:

• exercise and physical exertion
• anxiety, fear, excitement and stress
• caffeine, energy drinks, nicotine and alcohol (including the next day)
• decongestants such as pseudoephedrine, asthma inhalers, ADHD stimulants and some diet pills
• cannabis, cocaine and amphetamines
• fever: heart rate rises about 10 bpm for each 1 °C (about 1.8 °F) of fever
• dehydration and hot weather
• pregnancy, when resting heart rate rises by 10 to 20 bpm
• pain

Medical causes

• Hyperthyroidism: a persistently fast pulse with weight loss, tremor, sweating, heat intolerance and anxiety.
• Anemia: the heart pumps faster to deliver enough oxygen; with tiredness and pale skin.
• Infection and sepsis: a fast heart rate is an early sign of serious infection.
• Low blood sugar: sweating, shaking and a racing heart.
• Blood loss and low blood pressure.
• Pulmonary embolism: sudden breathlessness and fast heart rate.
• Heart failure and lung disease.
• POTS: heart rate rises by 30 bpm or more (40 in teens) within 10 minutes of standing, with dizziness, fatigue and brain fog.
• Alcohol or benzodiazepine withdrawal.

Abnormal heart rhythms

AFib matters because it raises stroke risk about fivefold, even if symptoms are mild. Ventricular tachycardia can deteriorate into cardiac arrest.

How doctors find the cause

A doctor will ask when it happens, how it starts and stops, whether the rhythm is regular, what you were doing, and about caffeine, alcohol, medicines and drugs, plus symptoms such as fainting or chest pain. They will check pulse, blood pressure (lying and standing), and listen to the heart.

Tests may include:

• ECG: a 12-lead recording, ideally during symptoms
• ambulatory monitoring: a 24 to 48-hour Holter monitor, a 2-week patch, or an event monitor for infrequent episodes; smartwatch ECGs can also help
• blood tests: blood count, thyroid function, electrolytes, kidney function, and glucose
• echocardiogram to check heart structure and function
• exercise test or tilt-table test in some cases

How to slow a rapid heartbeat

In the moment

• Sit or lie down, and breathe slowly: in for 4 seconds, out for 6 seconds.
• Drink water if you may be dehydrated.
• For known SVT, vagal maneuvers taught by your doctor can stop an episode: bearing down as if straining (Valsalva) for 15 seconds, or the modified Valsalva, where you strain then lie back with legs raised. Splashing ice-cold water on your face is another option.

Longer term

• Cut down caffeine, energy drinks and alcohol, and stop smoking or vaping.
• Review medicines and supplements with a pharmacist.
• Treat the cause: thyroid treatment, iron for anemia, managing anxiety, increased fluids and salt for POTS (if advised).
• Regular aerobic exercise lowers resting heart rate over time.

Treatments for arrhythmias

• Medicines: beta blockers or calcium channel blockers to control rate; antiarrhythmics to restore rhythm; blood thinners for AFib to prevent stroke.
• Catheter ablation: a procedure that destroys the tissue causing the abnormal rhythm; often curative for SVT and atrial flutter, and widely used for AFib.
• Cardioversion: an electrical shock or medicine to reset the rhythm.
• Implantable defibrillator for people at risk of dangerous ventricular rhythms.

Frequently asked questions

What heart rate is too high at rest?

For adults, a resting heart rate consistently over 100 bpm is considered fast and worth checking. A rate that stays above about 150 bpm at rest, or any fast rate with chest pain, fainting or severe breathlessness, needs emergency care.

Why is my heart racing when I'm resting?

Common reasons are anxiety, caffeine, dehydration, fever, alcohol the night before, and medicines like decongestants. If it happens often, causes such as an overactive thyroid, anemia or an arrhythmia like SVT or atrial fibrillation should be checked with an ECG and blood tests.

Can anxiety cause a rapid heartbeat?

Yes. Anxiety and panic release adrenaline, which can push the heart rate to 120 bpm or higher, with pounding, sweating and breathlessness. It usually settles within minutes. Episodes that start and stop abruptly, or happen without anxiety, should be checked for an arrhythmia.

Is a rapid heartbeat dangerous?

Usually not when it is a normal response to exercise, stress or caffeine. It can be dangerous when caused by arrhythmias like ventricular tachycardia, untreated atrial fibrillation, blood loss or a blood clot in the lungs, especially with chest pain, fainting or breathlessness.

How can I tell if my fast heartbeat is AFib?

AFib usually feels irregular and chaotic rather than a steady fast beat. Your pulse will be uneven when you check it. Many smartwatches can detect irregular rhythms. Only an ECG can confirm AFib, so see a doctor promptly if you notice an irregular pulse.