Bradycardia (Slow Heart Rate)

What heart rate is too low?

A normal resting heart rate for adults is 60 to 100 bpm. Rates below 60 are technically bradycardia, but whether that is a problem depends on the person:

Children have faster normal rates. A newborn's resting rate is typically above 100, so a slow rate in a baby or child is assessed against age-specific ranges by a pediatrician.

The key question is not the number alone but whether the heart rate rises appropriately when you are active and whether you have symptoms.

Symptoms of a slow heart rate

When the heart beats too slowly to meet the body's needs, blood flow to the brain and muscles drops. Symptoms include:

• Dizziness or lightheadedness
• Fainting or near-fainting (syncope)
• Tiredness and getting worn out easily
• Shortness of breath, especially on exertion
• Chest pain or pressure
• Confusion or memory problems, sometimes mistaken for aging in older adults
• Being unable to exercise as usual because the heart rate does not speed up

Common causes

Normal and harmless

• Physical fitness: training strengthens the heart and increases vagal tone, so each beat pumps more blood.
• Sleep: heart rate normally falls by 10 to 20 percent or more at night.
• Vasovagal reflexes: straining, vomiting, pain or seeing blood can briefly slow the heart.

Medicines

Beta-blockers (such as metoprolol), calcium channel blockers (verapamil, diltiazem), digoxin, amiodarone, ivabradine, clonidine, some eye drops for glaucoma, opioids and lithium can all slow the heart.

Heart rhythm problems

• Sick sinus syndrome: the heart's natural pacemaker becomes unreliable with age, sometimes alternating slow and fast rhythms.
• Heart block: signals are delayed or blocked between the upper and lower chambers.
• Heart attack: particularly involving the right coronary artery, which supplies the conduction system.

Other medical causes

• Hypothyroidism (underactive thyroid)
• High potassium from kidney disease or some medicines
• Hypothermia
• Sleep apnea, which causes slowing during breathing pauses
• Raised pressure in the skull after head injury or bleeding, where a slow pulse with high blood pressure is a dangerous sign
• Infections such as Lyme disease and myocarditis
• Eating disorders with very low body weight

How to check your pulse

1. Sit quietly for 5 minutes.
2. Place two fingers on the inside of your wrist below the thumb, or at the side of your neck.
3. Count the beats for 30 seconds and multiply by 2. If the rhythm is irregular, count for a full 60 seconds.

Smartwatches and pulse oximeters are generally accurate at rest, but they can undercount if the rhythm is irregular or if the device is loose. If a device shows a low rate and you feel unwell, check manually and seek care.

How doctors evaluate a slow heart rate

A doctor will ask about symptoms, fitness, medicines, sleep and thyroid symptoms, and examine your heart and blood pressure. Tests usually include:

• ECG: shows the rhythm and any heart block
• Holter or longer-term monitor: records the rhythm for 24 hours to several weeks to catch intermittent slowing
• Exercise test: checks whether the heart rate rises normally
• Blood tests: thyroid function, potassium and other electrolytes, and drug levels such as digoxin
• Echocardiogram: checks heart structure and pumping

See bradycardia as a condition for details on types, pacemakers and long-term treatment.

What you can do

• If you feel well and are active, a slow pulse usually needs no action beyond mentioning it at your next checkup.
• Do not stop prescribed heart medicines on your own. Ask your doctor whether the dose should be reviewed.
• Get up slowly from lying or sitting if you feel lightheaded.
• Keep a log of readings and any symptoms to show your doctor.
• Treat contributing problems such as sleep apnea and thyroid disease.

Frequently asked questions

What heart rate is too low?

For most adults, a resting rate under 60 bpm is called bradycardia, but rates in the 50s, and in the 40s in athletes or during sleep, are often normal. A rate below 50 bpm with dizziness, fainting or breathlessness, or below 40 bpm while awake, needs prompt medical assessment.

Is a heart rate in the 40s dangerous?

It depends. In a fit person who feels well, or during sleep, a rate in the 40s can be normal. In someone who feels dizzy, faint, short of breath or unusually tired, it may mean a rhythm problem, a medicine effect or a thyroid issue and should be checked soon.

Why is my heart rate low when I sleep?

During sleep the parasympathetic nervous system slows the heart, so rates of 40 to 60 bpm are common and healthy. Very low rates with long pauses, especially with loud snoring and breathing pauses, can be linked to sleep apnea and are worth discussing with a doctor.

Can anxiety cause a low heart rate?

Anxiety usually speeds the heart up. Some people have a vasovagal reaction to fear, pain or the sight of blood, which briefly slows the heart and lowers blood pressure, causing fainting. A persistently slow rate is not caused by anxiety.

Can dehydration cause a slow heart rate?

Dehydration usually causes a faster heart rate, not a slower one. However, severe vomiting or diarrhea can upset potassium and other electrolytes, which can affect heart rhythm. A slow pulse with dehydration symptoms should be checked.