A low pulse, meaning a resting heart rate below 60 beats per minute, can be completely normal or a sign that something needs attention. The difference comes down to whether you feel fine or you’re experiencing symptoms like dizziness, fatigue, or fainting. In many cases, a low pulse simply reflects a heart that’s efficient at its job. In others, it points to a medication side effect, a thyroid problem, or an electrical issue in the heart itself.
What Counts as a Low Pulse
For adults and adolescents, a normal resting heart rate falls between 60 and 100 beats per minute. Anything below 60 is technically bradycardia. But that threshold is a guideline, not a hard rule. Plenty of healthy people walk around with a resting pulse in the 50s or even 40s without any problems.
Children have naturally faster heart rates. A newborn’s normal range is 100 to 205 bpm, a toddler’s is 98 to 140, and school-age kids typically fall between 75 and 118. So a heart rate of 70 in a five-year-old is more concerning than the same number in a 30-year-old. Context matters enormously when evaluating whether a pulse is truly “low.”
Fitness Is the Most Common Harmless Cause
If you exercise regularly, especially endurance activities like running, cycling, or swimming, a low resting heart rate is expected and healthy. Years of cardiovascular training physically change the heart. It grows larger, fills with more blood per beat, and contracts more forcefully. Because each heartbeat pumps a greater volume of blood, the heart doesn’t need to beat as often to deliver oxygen to your body.
This adaptation is driven partly by increased activity of the branch of your nervous system responsible for rest and recovery, which naturally slows heart rate. Endurance athletes commonly have resting pulses in the 40s or 50s. Some elite athletes dip into the high 30s. As long as there are no symptoms, this is a sign of cardiovascular efficiency, not disease.
Medications That Slow Heart Rate
A low pulse is a known side effect of several widely prescribed drug classes. If you recently started a new medication and noticed your heart rate drop, the medication is a likely explanation.
- Blood pressure medications: Beta-blockers are among the most common culprits, with bradycardia reported in up to 25% of users. Calcium channel blockers like diltiazem and verapamil also slow the heart, affecting roughly 4 to 16% of people taking them. Clonidine, another blood pressure drug, causes a low pulse in 5 to 17% of users.
- Heart rhythm drugs: Medications prescribed to control irregular heartbeats, such as amiodarone and flecainide, can overcorrect and slow the heart too much.
- Certain antidepressants: Some SSRIs, particularly citalopram and escitalopram, have been linked to bradycardia in a small percentage of users.
- Digoxin: Used for heart failure and certain rhythm problems, digoxin directly slows heart rate and can push it too low, especially if levels build up in the bloodstream.
- Alzheimer’s medications: Donepezil, commonly prescribed for dementia, causes bradycardia in anywhere from less than 1% to nearly half of patients depending on the study.
If you suspect a medication is behind your low pulse, don’t stop taking it on your own. A dosage adjustment or switch to a different drug is often all that’s needed.
Thyroid Problems
An underactive thyroid (hypothyroidism) is one of the most common metabolic causes of a slow heart rate. Thyroid hormone directly influences how heart muscle cells function. It controls the activity of ion channels that regulate sodium, potassium, and calcium flow in and out of heart cells, and it even governs the genes responsible for the heart’s internal pacemaker rhythm.
When thyroid hormone levels drop, the heart muscle contracts less forcefully, relaxes more slowly between beats, and the natural pacemaker activity slows down. The result is a pulse that’s lower than your usual baseline, often accompanied by other hypothyroid symptoms like fatigue, weight gain, cold sensitivity, and dry skin. Treating the thyroid condition with hormone replacement typically brings heart rate back to normal.
Electrical Problems in the Heart
Your heartbeat is triggered and coordinated by an electrical system. Two types of electrical malfunction account for the majority of cases where a low pulse needs medical intervention.
The first is sinus node dysfunction. The sinus node is your heart’s natural pacemaker, a small cluster of cells that fires the electrical signal starting each heartbeat. When this node doesn’t fire reliably, the heart rate drops or pauses unpredictably. Aging, scarring from prior heart disease, or inflammation can damage these cells over time.
The second is heart block, where the electrical signal that starts in the upper chambers gets delayed or completely interrupted before reaching the lower chambers. Heart block comes in degrees. A mild delay might cause no symptoms at all. A complete block, where the signal never reaches the lower chambers, forces the heart to rely on a much slower backup rhythm, often in the 30s or 40s.
Together, sinus node dysfunction and heart block are the primary reasons people receive permanent pacemakers. While these conditions are rarely immediately life-threatening, they can cause fainting, severe fatigue, and in some cases acute heart failure if left untreated.
Electrolyte Imbalances
Potassium plays a central role in every heartbeat. When blood potassium levels climb too high, a condition called hyperkalemia, it disrupts the heart’s electrical signaling. At potassium levels of 6.0 milliequivalents per liter and above (normal is roughly 3.5 to 5.0), the heart can slow dramatically. In one study of emergency patients with severe hyperkalemia, the median heart rate was just 43 beats per minute with an average potassium of 7.1.
The electrical disruption shows up on an EKG as tall, peaked T-waves, widening of the heartbeat signal, and sometimes a shift to a slower backup rhythm called a junctional rhythm. High potassium can result from kidney disease, certain medications (including some blood pressure drugs), severe dehydration, or excessive potassium supplementation. This is one of the more urgent causes of a low pulse because the heart rhythm can deteriorate quickly if potassium isn’t brought back into range.
Sleep Apnea and Nighttime Bradycardia
If your low pulse mainly occurs at night or your partner has noticed pauses in your breathing during sleep, obstructive sleep apnea could be involved. During an apnea episode, the upper airway collapses and blocks airflow. The body responds with what’s essentially a diving reflex: blood vessels constrict to prioritize oxygen delivery to vital organs, blood pressure spikes, and the nervous system triggers a reflex slowing of the heart.
This cycle of oxygen deprivation followed by reflexive bradycardia can repeat dozens of times per hour throughout the night. Treating sleep apnea, usually with a CPAP device, resolves the nighttime heart rate drops and reduces the long-term cardiovascular strain.
When a Low Pulse Needs Attention
A low pulse by itself isn’t necessarily a problem. The critical question is whether it’s causing symptoms. A well-trained athlete with a resting pulse of 45 who feels great has nothing to worry about. But the same heart rate in someone who feels lightheaded when standing, unusually exhausted, short of breath during normal activities, or who has fainted needs evaluation.
A resting heart rate below 35 to 40 bpm with any symptoms warrants prompt medical attention. Even without symptoms, a pulse that has dropped noticeably from your personal baseline deserves investigation, particularly if you have risk factors like thyroid disease, heart disease, or recent medication changes. A simple EKG, blood work checking thyroid function and electrolytes, and sometimes a wearable heart monitor that records your rhythm over 24 to 48 hours are usually enough to identify the cause.