Rapid Heart Rate (Tachycardia): Causes and When to Worry

What counts as a fast heart rate

To check your pulse, place two fingers on the inside of your wrist below the thumb, count beats for 30 seconds and double it. Smartwatches are accurate for rate but can miss or misidentify rhythms.

Normal reasons for a fast heartbeat

The heart speeds up appropriately in response to:

• exercise and physical exertion
• excitement, fear, anger or anxiety
• caffeine, energy drinks, nicotine and alcohol
• fever: heart rate rises about 10 beats per minute for each 1 °C of fever
• pregnancy: resting rate rises by 10 to 20 beats
• standing up quickly

Medical causes

Conditions outside the heart

• Dehydration or blood loss: the heart beats faster to maintain blood pressure.
• Anemia: fewer red cells to carry oxygen, so the heart works harder; also tiredness and breathlessness.
• Overactive thyroid: fast pulse at rest, weight loss, sweating, tremor and anxiety.
• Anxiety and panic attacks: sudden racing heart with fear, breathlessness and tingling.
• Infections and sepsis.
• Pulmonary embolism: a lung clot causing sudden breathlessness and a fast pulse.
• Low blood sugar.
• Medicines and drugs: asthma inhalers, decongestants (pseudoephedrine), thyroid hormone in excess, some antidepressants, stimulants for ADHD, cocaine and amphetamines; withdrawal from alcohol or beta-blockers.

Heart rhythm problems (arrhythmias)

Postural tachycardia syndrome (POTS)

In POTS, heart rate rises by 30 beats per minute or more within 10 minutes of standing (40 or more in teenagers), without a big drop in blood pressure. Dizziness, fatigue, brain fog and palpitations are common. It mostly affects young women and sometimes follows a viral infection.

When to worry about a fast heart rate

Worry less if it starts with an obvious trigger, stays below about 120 to 130, and settles within minutes of resting. Get help when:

• it is accompanied by chest pain, fainting, severe breathlessness or confusion
• it starts and stops suddenly, like a switch
• the pulse feels irregular
• your resting rate is consistently above 100 without explanation
• you have known heart disease

How doctors find the cause

A doctor will ask how episodes start and stop, how long they last, triggers, caffeine, alcohol, drugs, medicines, and family history of heart problems or sudden death. They check your pulse, blood pressure (lying and standing) and listen to your heart and lungs.

Tests:

• ECG: captures the rhythm. If you can record an ECG during an episode, on a smartwatch or at urgent care, it is extremely useful.
• Ambulatory monitoring: a Holter monitor for 24 to 48 hours, a patch for up to 2 weeks, or an event recorder for longer.
• Blood tests: blood count, thyroid function, electrolytes, kidney function, and sometimes D-dimer or troponin.
• Echocardiogram: an ultrasound of heart structure and function.
• Tilt table test for suspected POTS.
• Electrophysiology study to map and treat certain arrhythmias.

How to slow a rapid heart rate

During an episode

• Sit or lie down and breathe slowly.
• Vagal maneuvers can stop some SVT episodes: bear down as if straining for 15 seconds (Valsalva), or splash ice-cold water on your face. The "modified Valsalva", straining while sitting, then lying flat with legs raised, works better. Ask your doctor before relying on these.
• Drink water if you might be dehydrated.
• Do not use these techniques instead of calling 911 if red flags are present.

Long-term treatment

• Treat the underlying cause: rehydration, iron for anemia, thyroid treatment, stopping triggering medicines.
• Lifestyle: cut back on caffeine, energy drinks and alcohol; stop smoking; manage stress; get regular exercise.
• Medicines: beta-blockers or calcium channel blockers slow the heart; antiarrhythmics control rhythm; blood thinners reduce stroke risk in atrial fibrillation.
• Catheter ablation: destroys the small area of tissue causing SVT, atrial flutter or atrial fibrillation; often curative for SVT.
• POTS: increased fluids and salt, compression garments, graded exercise and sometimes medicines.

Frequently asked questions

What is a dangerous heart rate?

A resting heart rate over 100 is considered fast, and over 150 that does not settle at rest needs urgent assessment. Any fast heart rate is dangerous if it comes with chest pain, fainting, severe breathlessness or confusion. Call 911 in those situations.

Why is my heart rate high when resting?

Common reasons include dehydration, caffeine, anxiety, fever, anemia, an overactive thyroid, poor fitness, medicines such as decongestants or inhalers, and alcohol. If your resting rate is often above 100 without explanation, see a doctor for an ECG and blood tests.

Can anxiety cause a fast heart rate?

Yes. Anxiety and panic release adrenaline, which raises heart rate, often to 100 to 140. It usually settles as the anxiety eases. A heart rate that starts and stops abruptly or is irregular should be checked for a rhythm problem.

How can I lower my heart rate quickly?

Sit down, breathe slowly and deeply, and drink water if you are dehydrated. For known SVT, vagal maneuvers such as the modified Valsalva can stop an episode. Over time, regular exercise, less caffeine and alcohol, and managing stress lower resting heart rate.

Is a fast heart rate a sign of a heart attack?

It can occur during a heart attack, but chest pain or pressure, breathlessness, sweating and pain spreading to the arm or jaw are the main warning signs. A fast heart rate alone is far more often from another cause.