A resting heart rate of 45 beats per minute falls below the standard “normal” range of 60 to 100 bpm, but whether it’s good or concerning depends almost entirely on how you feel. For physically active people, 45 bpm can be a sign of a strong, efficient heart. For others, it could signal an underlying issue worth investigating.
Why 45 BPM Can Be Perfectly Healthy
The American Heart Association notes that athletes and highly active people can have resting heart rates as low as 40 bpm. When you exercise regularly, your heart muscle grows stronger and pumps more blood with each beat. That means it doesn’t need to beat as often to deliver oxygen throughout your body. A lower resting heart rate in this context generally means your heart is in better condition, not worse.
This is sometimes called “athletic bradycardia,” and it’s common in endurance athletes like runners, cyclists, and swimmers. If you’re active and feel fine at 45 bpm, your heart is simply working more efficiently than average.
When 45 BPM Is a Problem
The number alone doesn’t tell the full story. What matters is whether your brain and organs are getting enough oxygen. If a slow heart rate is limiting blood flow, you’ll typically notice symptoms like:
- Dizziness or lightheadedness
- Unusual fatigue, especially during physical activity
- Fainting or near-fainting episodes
- Shortness of breath
- Confusion or difficulty concentrating
- Chest pain
If you’re experiencing any of these alongside a heart rate of 45, that combination is worth taking seriously. The Cleveland Clinic recommends seeking medical care if a low heart rate is paired with symptoms like chest pain, trouble breathing, or dizziness. A heart rate that drops below 40 bpm unexpectedly also warrants prompt attention.
Your Heart Rate Drops Even Lower During Sleep
If you noticed 45 bpm on a fitness tracker overnight, that’s likely nothing to worry about. A healthy adult’s heart rate during sleep typically falls to 50 to 75 bpm, and rates as low as 40 bpm during deep sleep are considered within the normal range. Well-trained endurance athletes can dip into the 30s while sleeping because their nervous system is so well-conditioned.
Sleeping heart rates below 40 bpm in non-athletes, or rates in the 20s for anyone, are worth discussing with a doctor. Repeated pauses in breathing during sleep (obstructive sleep apnea) can also cause the heart rate to drop unusually low at night, so persistent nocturnal bradycardia sometimes leads to a sleep study.
Common Causes Beyond Fitness
If you’re not particularly athletic and your resting heart rate sits at 45, several things could explain it. Medications are one of the most common culprits. Blood pressure drugs like beta-blockers and certain calcium channel blockers work by slowing the heart rate and can easily bring it into the 40s. Some antidepressants and heart rhythm medications do the same. If you started or adjusted a medication recently and noticed your heart rate drop, that’s a likely connection to bring up with your prescriber.
An underactive thyroid is another well-known cause. When your thyroid produces too little hormone, your heart rate slows and your arteries become less flexible. A simple blood test can check for this. Electrolyte imbalances, particularly with potassium, can also affect your heart’s electrical system and lower your rate.
How Doctors Evaluate a Slow Heart Rate
If your heart rate of 45 is new, unexplained, or accompanied by symptoms, a doctor will typically start with an electrocardiogram (ECG), which measures your heart’s electrical activity through sensors placed on your chest. This is the primary tool for diagnosing bradycardia and can reveal whether the slow rate is coming from a healthy heart or an electrical signaling problem.
If a standard ECG looks normal but you’re still having symptoms, you may be asked to wear a portable heart monitor. A Holter monitor records your heart rhythm continuously for a day or more during normal activities. An event recorder works similarly but can be worn for up to 30 days and captures data when you press a button during symptoms. Blood work to check thyroid function and electrolyte levels is also standard.
For people who’ve fainted, a tilt table test can help determine how your heart and nervous system respond to changes in position. And if symptoms seem tied to physical exertion, a stress test on a treadmill or stationary bike can reveal problems that only surface during exercise.
The Bottom Line on Treatment
Current cardiology guidelines from the American College of Cardiology and the American Heart Association emphasize that there’s no fixed heart rate number where treatment automatically kicks in. The key factor is whether symptoms correlate with the slow rate. A 45 bpm heart rate in someone who feels great requires no intervention. The same rate in someone who’s dizzy and exhausted could point to a condition that needs treatment.
If your heart rate is between 40 and 60 bpm and you have no symptoms, there’s generally no reason to worry. But it’s still worth mentioning to your doctor at your next visit so they can rule out reversible causes like thyroid dysfunction or medication side effects. For people whose bradycardia stems from a problem with the heart’s electrical wiring, a pacemaker is sometimes recommended, but only when the slow rate is clearly causing symptoms or when specific types of electrical blockages are identified.