When a Low Heart Rate Is Normal and When to Get Help

How Low Is Too Low? Heart Rate Thresholds and Red Flags

A resting heart rate below 60 beats per minute meets the traditional medical definition of bradycardia, but rates down to 40 beats per minute without symptoms are usually no reason to worry. The resting heart rate guide on this site gives the normal adult range as 60 to 100 beats per minute.

In the 2018 ACC/AHA/HRS bradycardia guideline, sinus bradycardia is defined as a sinus rate under 50 beats per minute while awake. The guideline also identifies a sinus pause when the sinus node depolarizes more than three seconds after the prior atrial depolarization. Chronotropic incompetence occurs when the heart cannot increase rate commensurate with activity.

According to Cleveland Clinic, bradycardia simply means the heart beats fewer than 60 times per minute. Cleveland Clinic notes that slow rates are normal for some people. Treating the underlying cause can often restore a normal heart rate.

Cleveland Clinic outlines clear emergency thresholds: "Call 911 or your local emergency services number if: You have a low heart rate along with symptoms like chest pain, heart palpitations, trouble breathing or dizziness [or] Your heart rate falls below 40 beats per minute (and this isn't usual for you)."

Cleveland Clinic adds: "If your heart rate drops into the 30s, that's getting into dangerous territory. You might not get enough oxygen to your brain. This can cause fainting, lightheadedness and shortness of breath. Seek medical attention right away."

When a Low Heart Rate Is Normal

Cleveland Clinic says a slow rate is common among athletes and that it is normal for the heart rate to drop a bit during sleep. Athletic conditioning enables the heart muscle to pump blood more efficiently with each contraction. Cleveland Clinic explains that an athlete's heart "can beat more slowly while still sending enough blood to your body."

Cleveland Clinic says that for many people bradycardia causes no symptoms, which is common among athletes with a low heart rate. Cleveland Clinic calls this sleep-time slowing sinus bradycardia, meaning the heart's electrical system is still working appropriately.

The 2018 ACC/AHA/HRS guideline rates permanent pacing Class III (Harm) in two situations: people without symptoms whose sinus bradycardia or pauses come from physiologically elevated parasympathetic tone, and sleep-related sinus bradycardia unless other reasons for pacing are present.

Heart rate variability, a separate measure, is covered on the heart rate variability page.

Symptoms of a Low Heart Rate

Symptoms of a low heart rate develop when the heart fails to pump enough blood to meet metabolic demands.

Cleveland Clinic lists these symptoms:

• Feeling dizzy or lightheaded
• Fainting
• Confusion or trouble focusing
• Shortness of breath
• Chest pain
• Fatigue
• Heart palpitations

If your heart rate is unexpectedly low and you experience these symptoms, seek medical care right away.

MedlinePlus says that when the heart beats too slowly, "your body and brain may not get enough oxygen," which can bring lightheadedness, tiredness, fainting spells and shortness of breath.

Reports from CardioSmart indicate that uncorrected bradycardia can lead to heart failure or sudden cardiac arrest. These outcomes occur when cardiac output cannot sustain tissue perfusion.

What Causes a Low Heart Rate

A low heart rate stems from intrinsic conduction disease, systemic conditions, electrolyte abnormalities, or prescription drug therapies. Cleveland Clinic and the 2018 guideline list diverse reversible and chronic etiologies.

Age-dependent progressive fibrosis of the sinus nodal tissue represents the primary cause of sinus node dysfunction. Conduction disorders become more common after age 70.

According to the National Heart, Lung, and Blood Institute (NHLBI), sick sinus syndrome can cause a slow or fast heart rate. Third-degree AV block can cause serious symptoms including a very slow heart rate, fainting, and chest pain.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) notes that thyroid hormones affect even the way the heart beats. An underactive thyroid gland produces a slowed heart rate alongside fatigue, weight gain, and cold intolerance.

The 2018 guideline notes that sleep-disordered breathing and nocturnal bradycardia are both relatively common, and recommends screening for sleep apnea symptoms when bradycardia is documented or suspected during sleep. For documented obstructive sleep apnea, the guideline recommends continuous positive airway pressure and weight loss.

CardioSmart reports that sleep apnea can cause bradycardia, make it worse, or do both. Multiple prescription drugs lower resting heart rates. The 2018 guideline lists beta-blockers, non-dihydropyridine calcium channel blockers, digoxin, antiarrhythmic drugs and lithium among potentially reversible causes.

Electrolyte abnormalities such as hyperkalemia, hypokalemia, and hypoglycemia also disrupt sinus node activity.

Tests Doctors Use

Diagnostic evaluation of a low heart rate combines resting electrocardiography, extended rhythm monitoring, blood chemistry, and imaging. Cleveland Clinic notes that a standard ECG only tracks heart activity for less than a minute, so it might not capture a low heart rate episode, and a provider may recommend an ambulatory monitor you wear during daily life.

MedlinePlus explains that a Holter monitor continuously records heart rhythms for 24 to 48 hours. MedlinePlus lists "slow heart rate (bradycardia)" among the rhythms it can record.

The 2018 ACC/AHA/HRS guideline establishes Class I recommendations for a comprehensive history, physical examination, resting ECG, and ambulatory monitoring. Monitor selection depends on the frequency of symptoms.

For infrequent symptoms occurring more than 30 days apart, an implantable cardiac monitor receives a Class IIa recommendation. Exercise ECG testing carries a Class IIa recommendation for patients with exercise-related symptoms. Echocardiography is recommended when clinicians suspect structural heart disease.

For asymptomatic sinus bradycardia without signs of structural heart disease, routine cardiac imaging is not indicated. Blood tests evaluate serum electrolytes and thyroid hormone. Thyroid hormone testing is outlined in the guide on thyroid panel blood tests.

Sleep studies evaluate suspected obstructive sleep apnea.

Treating a Low Heart Rate With Medication Changes or a Pacemaker

Bradycardia treatment focuses on eliminating reversible causes, modifying drug regimens, or providing permanent pacing when symptoms persist. Cleveland Clinic states that healthy individuals without symptoms may not need treatment. Bradycardia is treatable and often curable.

If a prescription medicine slows the pulse excessively, clinicians adjust or change the drug. Cleveland Clinic emphasizes that patients must never change prescription medications on their own. In emergency hospital scenarios, intravenous medications such as atropine provide temporary rate support.

A slow pulse is judged by what comes with it more than by the number: the cardiology guideline sets no minimum heart rate for pacing in sinus node dysfunction and instead asks whether symptoms line up with the slow beats. The number matters on its own only at the bottom of the range, where Cleveland Clinic draws its 911 line at 40 bpm.

For sinus node dysfunction, permanent pacing receives a Class I recommendation when symptoms correlate directly with bradycardia after reversible causes are excluded. In contrast, the guideline recommends permanent pacing for acquired second-degree Mobitz type II, high-grade, or third-degree AV block not caused by reversible or physiologic causes, regardless of symptoms.

The NHLBI notes that pacemakers most commonly treat slow beating or pauses causing fainting. Beta blockers can slow the heartbeat too much, and a pacemaker maintains rate when medication remains necessary. MedlinePlus describes a pacemaker as a small, battery-operated device that senses when the heart beats too slowly.

Implantation takes about one hour under sedation, and most patients return home within one day. MedlinePlus says you may be advised not to lift more than 10 to 15 pounds or raise the arm above the shoulder for several weeks. Pacemaker batteries last between 6 and 15 years.

Discuss an unexpectedly low heart rate with a qualified healthcare provider to establish appropriate monitoring and care.