Is a Resting Heart Rate of 45 Too Low?

On its own, usually not. A resting heart rate of 45 is lower than most adults': in US national data, 95 percent of men aged 40 to 59 had a seated pulse above 52 beats per minute and 95 percent of women above 56. The cardiology societies' bradycardia guideline treats a sinus rate under 50 as one possible sign of a sinus node problem, but it says the rate alone should not be used to make that diagnosis, and that slow sinus rhythm without symptoms has not been associated with adverse outcomes. What changes the picture is symptoms the guideline ties to a slow heart rate, such as fainting, near-fainting, dizziness or lightheadedness, and context: endurance training, sleep and some medications all lower heart rate, and a wearable's resting figure is usually taken while you sleep.

Where 45 sits against other adults

Lower than about 95 percent of adults. In US national survey data, the 5th percentile of seated resting pulse was 52 beats per minute for men aged 40 to 59 and 56 for women, and 50 for men and 56 for women aged 60 to 79. People with a condition or medication affecting pulse were excluded, so these are figures for a healthy population.

Rare and abnormal are different things here. In four Dutch population studies cited by the bradycardia guideline, the lowest 2nd percentile of heart rate in adults aged 20 to 90 ran from 40 to 55 beats per minute depending on sex and age, which puts a healthy adult at 45 at the low edge of that spread.

Age changes this less than it changes most numbers. Adult resting pulse barely moves across the decades in the same survey, which is covered in resting heart rate by age, ages 40 to 59 and ages 60 to 79.

What the bradycardia guideline says about a rate under 50

Textbooks usually draw the line at 60, and the US National Institutes of Health defines bradycardia as a heart rate under 60 beats per minute in adults other than well-trained athletes, but population studies often use 50. The guideline from the American College of Cardiology, American Heart Association and Heart Rhythm Society chose a sinus rate under 50 as one potential component of sinus node dysfunction.

It then sets two limits on that number. A slow sinus rate on its own should not be used to diagnose sinus node dysfunction, and with rare exceptions the only reason to consider treating it is symptoms. The guideline also states that sinus bradycardia without symptoms has not been associated with adverse outcomes, and that it is the most common slow rhythm seen during sleep.

Symptoms, in the guideline's own definition, means a slow rhythm directly causing fainting or near-fainting, passing dizziness or lightheadedness, heart failure symptoms, or confusion from reduced blood flow to the brain. Fatigue fits less cleanly: the guideline notes that it has many causes and is hard to tie to a modestly slow resting rate. Medications are among the reversible causes it lists, with beta blockers as an example.

When a low rate is a sign of fitness

Endurance training slows the resting heart, and very low rates are common in trained athletes. Among 465 current and former elite endurance athletes, 38 percent had a minimum heart rate of 40 or lower on 24-hour monitoring, 2 percent dropped to 30 or lower, and a quarter had pauses of 2 seconds or more. Over 5.5 years, neither the slow rates nor the pauses were associated with adverse outcomes (Circulation, 2026).

Genes played a part as well. Athletes with a lower genetic score for heart rate had lower minimum rates and about twice the odds of resting bradycardia after adjusting for age, sex and fitness. The group was young, with a median age of 23, so the study shows that a very slow rate can be harmless in fit people. It does not show that every slow rate in a 55 or 65 year old reflects fitness.

Is a lower resting heart rate better for longevity?

On average, lower goes with lower risk. A review of the field describes a low resting heart rate as associated with health and longevity and a high rate with disease and adverse events, and reports that genetic studies using Mendelian randomization point to a causal link between resting heart rate and longevity (Scandinavian Journal of Clinical and Laboratory Investigation, 2019).

That evidence comes mostly from comparisons across the normal and high range. Across 46 studies and 1,246,203 people, each 10 beats per minute higher went with a relative risk of 1.09 for death from any cause (Canadian Medical Association Journal, 2016). It does not show that 45 is healthier than 55, and it does not describe a slow rate caused by a problem with the heart's electrical system. The resting heart rate desk rates the general link between a higher resting rate and worse cardiovascular health as Emerging.

A wearable's 45 is usually a sleeping number

Watches and rings mostly report the lowest heart rate of the day or the night. Garmin uses the lowest 30-minute average in a 24-hour period (Garmin support), and Oura reports both an average and a lowest overnight figure (Oura support). Heart rate falls further in sleep, and the guideline lists sleep among the states in which sinus bradycardia is seen. A ring showing 45 overnight and a nurse counting 45 at the wrist after four minutes of sitting, the way the survey percentiles above were taken, are measuring different moments.

The overnight figure itself is usually close. Against a simultaneous ECG in 13 adults over 536 nights, resting heart rate error averaged 1.67 percent for Oura Gen 3 and 1.94 percent for Oura Gen 4 (Physiological Reports, 2025). The more informative signal is a change from your own usual number: see elevated resting heart rate.

What this does not settle

The guideline exists to help diagnose and treat slow heart rhythms. It says nothing about what resting rate is ideal. No study cited here compares long-term outcomes for healthy adults at 45 against adults at 55, and the athlete cohort was young and highly trained. A single reading also carries no history: a long-standing low rate in someone who trains is a different situation from a recent drop that comes with dizziness or fainting.

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