Bradycardia is a resting heart rate below 60 beats per minute (bpm). A normal adult heart beats between 60 and 100 times per minute at rest, so anything under that lower threshold technically qualifies. But the number alone doesn’t tell the whole story. A heart rate in the 40s or 50s can be perfectly healthy in some people, while a rate of 55 might cause real problems in others.
When a Slow Heart Rate Is Normal
A resting heart rate between 40 and 60 bpm is common in healthy young adults, well-trained athletes, and during sleep. Nearly half of endurance athletes show bradycardia as a positive adaptation to training, with resting rates documented as low as 30 to 37 bpm in some runners. This happens because regular aerobic exercise makes the heart stronger and more efficient, so it pumps more blood with each beat and doesn’t need to beat as often.
Sleep is another time when your heart rate naturally drops well below 60. In studies tracking overnight heart rate, the minimum during sleep averaged around 53 bpm but ranged as low as 36 bpm in healthy individuals. This is a normal part of how your nervous system shifts gears at night, dialing down heart rate as your body rests and repairs.
When a Slow Heart Rate Becomes a Problem
Bradycardia becomes a medical concern when your heart beats too slowly to deliver enough oxygen to your brain and body. The symptoms reflect that oxygen shortfall:
- Dizziness or lightheadedness
- Fainting or near-fainting
- Unusual fatigue, especially during physical activity
- Shortness of breath
- Chest pain
- Confusion or memory problems
If you have a heart rate below 60 but feel fine, exercise without trouble, and aren’t experiencing any of these symptoms, your slow heart rate is likely harmless. The distinction between “bradycardia on paper” and “bradycardia that needs attention” comes down to whether it’s causing symptoms or affecting how well your organs function.
Emergency protocols generally flag a heart rate below 40 bpm with symptoms like fainting, low blood pressure, chest pain, or heavy sweating as requiring immediate intervention. That 40 bpm mark, combined with signs of poor blood flow, is the threshold where treatment becomes urgent.
Heart Rate Ranges in Children
Children have naturally faster heart rates than adults, so the definition of “too slow” shifts depending on age. A rate that’s perfectly normal in a teenager would be dangerously low in a newborn. Based on American Heart Association guidelines, here’s what’s expected:
- Newborn to 3 months: 85 to 205 bpm awake, 80 to 160 bpm asleep
- 3 months to 2 years: 100 to 190 bpm awake, 75 to 160 bpm asleep
- 2 to 10 years: 60 to 140 bpm awake, 60 to 90 bpm asleep
- Over 10 years: 60 to 100 bpm awake, 50 to 90 bpm asleep
A heart rate that drops below the low end of these ranges for a child’s age group is considered bradycardia for that child, even if the same number would be normal in an adult.
What Causes Bradycardia
When bradycardia isn’t a harmless athletic adaptation or sleep pattern, it usually traces back to a problem with the heart’s electrical system, a medication side effect, or a metabolic condition.
Electrical System Problems
Your heart has a built-in pacemaker, a cluster of cells called the sinus node, that sends electrical signals telling the heart when to beat. When this natural pacemaker malfunctions, the condition is called sinus node dysfunction or sick sinus syndrome. It can cause the heart to beat too slowly, pause for abnormally long stretches, or alternate between racing and crawling (sometimes called tachy-brady syndrome). One hallmark sign is a heart rate that fails to speed up appropriately during exercise, defined as reaching less than 80 percent of the expected heart rate response for your age.
The other common electrical problem involves heart block, where the signals generated by the sinus node get delayed or partially blocked before reaching the lower chambers of the heart. Depending on severity, this can cause mild slowing or dangerously low heart rates with long pauses between beats.
Medications
Several common medications slow the heart rate as either their intended effect or a side effect. Beta-blockers and calcium channel blockers, both widely prescribed for high blood pressure and heart conditions, are the most frequent culprits. Other heart rhythm medications can do the same. Outside of cardiac drugs, certain seizure medications, lithium (used for bipolar disorder), and some antidepressants can also lower heart rate enough to cause symptoms.
Thyroid and Metabolic Issues
An underactive thyroid (hypothyroidism) directly slows the heart. Low levels of thyroid hormone reduce the heart’s ability to contract forcefully and beat at an appropriate rate. This combination decreases the amount of blood pumped with each beat and can raise the risk of heart failure over time if left untreated. Electrolyte imbalances, particularly high potassium levels, can also interfere with the heart’s electrical signals and slow it down.
How Bradycardia Is Treated
Treatment depends entirely on the cause and whether you’re having symptoms. If a medication is responsible, adjusting the dose or switching to a different drug often resolves the problem. If hypothyroidism is driving the slow rate, thyroid hormone replacement typically brings the heart rate back to normal.
For bradycardia caused by an irreversible electrical problem in the heart, a pacemaker is the standard treatment. A pacemaker is a small device implanted under the skin near the collarbone that monitors your heart rhythm and delivers tiny electrical impulses to keep the rate from dropping too low. The procedure itself is relatively quick, and most people go home the same day or the next morning.
In an emergency where the heart rate drops dangerously low and blood pressure falls, hospital treatment focuses on restoring adequate heart rate and blood flow quickly, sometimes with medication given through an IV, and if that doesn’t work, temporary external pacing using electrode pads on the chest.
Checking Your Own Heart Rate
The simplest way to check your resting heart rate is to place two fingers on the inside of your wrist (just below the base of your thumb) and count the beats for 30 seconds, then multiply by two. Do this after sitting quietly for at least five minutes, ideally in the morning before caffeine or exercise. Many smartwatches and fitness trackers also measure resting heart rate continuously and can alert you to unusually low readings.
If your resting heart rate consistently reads below 60 and you’re experiencing fatigue, dizziness, or any of the symptoms listed above, that pattern is worth bringing to a doctor’s attention. A single low reading on its own, especially after sleep or deep relaxation, is rarely meaningful.