An abnormal heart rate is any resting heart rate that falls outside the standard range of 60 to 100 beats per minute (bpm) for adults, or any rhythm that is irregular regardless of speed. A heart beating too fast at rest (above 100 bpm) is called tachycardia, while one beating too slowly (below 60 bpm) is called bradycardia. Some irregular rhythms, like atrial fibrillation, can occur even when the overall rate looks close to normal. What counts as “abnormal” also depends on your age, fitness level, and what you were doing right before you checked.
Normal Resting Heart Rate by Age and Fitness
For most adults, a resting heart rate between 60 and 100 bpm is considered normal. But that range has important exceptions. Well-trained athletes often have resting rates in the 40s or 50s because their hearts pump blood more efficiently with each beat, so fewer beats are needed. A rate of 45 bpm in a competitive runner is typically healthy, while the same rate in a sedentary 70-year-old could signal a problem.
Children naturally run faster. Newborns can have resting rates above 120 bpm, and toddlers commonly sit between 90 and 110. Heart rate gradually slows through childhood, settling into the adult range by the mid-teen years. During sleep, rates in both adults and children drop well below daytime norms, which is perfectly expected.
When the Heart Beats Too Fast: Tachycardia
Tachycardia means a resting heart rate above 100 bpm. Exercise, anxiety, or a cup of coffee can push your rate past 100 temporarily, and that’s not the same thing. The concern is when your heart stays fast while you’re sitting still, lying down, or doing nothing physically demanding.
Common triggers include stress, dehydration, high blood pressure, anemia, low blood sugar, and pregnancy. Caffeine promotes the release of stress hormones that raise heart rate and blood pressure, and in people who are susceptible, it can trigger atrial fibrillation, a chaotic electrical pattern in the upper chambers that produces a rapid, irregular heartbeat. Tobacco, alcohol, and certain medications can have similar effects.
Tachycardia can also point to underlying heart conditions like coronary artery disease or problems with the heart’s electrical wiring. If a fast rate comes with chest pain, shortness of breath, lightheadedness, or fainting, those symptoms together suggest the heart isn’t pumping effectively despite working harder.
When the Heart Beats Too Slowly: Bradycardia
Bradycardia is a heart rate below 60 bpm at rest. In many people, especially younger adults and athletes, a slow heart rate is simply a sign of cardiovascular fitness. During sleep, rates in the 40s and 50s are common and normal.
Bradycardia becomes a problem when the heart can’t deliver enough blood to meet the body’s needs. That typically shows up as fatigue, dizziness, confusion, or fainting. In older adults, a slow rate may result from age-related changes to the heart’s natural pacemaker cells or from medications that deliberately slow the heart, such as certain blood pressure drugs. If a slow heart rate is causing symptoms, the underlying cause determines whether the fix is adjusting a medication or, in some cases, implanting a pacemaker.
Irregular Rhythms: Skipped Beats, AFib, and Flutter
Not all abnormal heart rates are simply too fast or too slow. Some involve irregular timing between beats.
- Premature heartbeats are extra beats that sneak in ahead of schedule, creating the sensation of a “skipped” or “fluttering” beat. When they originate in the upper chambers, they’re called premature atrial contractions (PACs). Most people experience them occasionally, and they’re usually harmless.
- Atrial fibrillation (AFib) is the most common sustained arrhythmia. Chaotic electrical signals cause the upper chambers to quiver instead of contracting in a coordinated way, producing an irregular and often fast heartbeat. AFib sometimes comes and goes on its own, but in other cases it persists until treated. The biggest risk is stroke, because blood can pool in the quivering chambers and form clots.
- Atrial flutter is similar to AFib but involves a more organized electrical circuit. It also carries an increased stroke risk.
Irregular rhythms can be tricky to catch because they may appear for minutes or hours and then disappear. You might feel palpitations, a racing sensation, or nothing at all.
What Influences Your Heart Rate Day to Day
Your heart rate isn’t a fixed number. It shifts throughout the day based on activity, emotions, temperature, hydration, and what you’ve consumed. Caffeine is one of the most common culprits behind a noticeably faster heartbeat. It stimulates the nervous system and, in large amounts, can push susceptible people into AFib. Lethal caffeine doses (above roughly 10 grams, far more than normal consumption) cause dangerous spikes in heart rate and blood pressure, but even moderate intake can be noticeable if you’re sensitive.
Dehydration reduces blood volume, forcing the heart to beat faster to maintain circulation. Stress and anxiety trigger the same fight-or-flight hormones that caffeine mimics. Fever raises heart rate by about 10 bpm for every degree of body temperature above normal. Even body position matters: standing up quickly can cause a brief spike as your cardiovascular system adjusts to gravity.
How to Check Your Own Heart Rate
Before measuring, sit quietly for a few minutes so your rate reflects true rest. You can check at two spots:
At your wrist: Turn one hand palm-up. Place the tips of your index and middle fingers from the other hand on the thumb side of your wrist, in the groove between the wrist bone and the tendon. Press lightly until you feel each beat. Pressing too hard can actually block blood flow and give you an inaccurate reading.
At your neck: Place two fingertips in the soft groove beside your windpipe on one side. Never press on both sides of your neck at once, as this can make you dizzy or faint. If you’ve been told you have plaque buildup in your neck arteries, skip this method entirely.
Count beats for a full 60 seconds using a clock or timer. Alternatively, count for 15 seconds and multiply by four. Pay attention to whether the rhythm feels steady or irregular, since spacing matters as much as speed.
How Abnormal Heart Rates Are Diagnosed
A standard electrocardiogram (EKG) records your heart’s electrical activity, but it only captures a few seconds. That’s useful when an abnormal rhythm is happening right then, but many arrhythmias come and go unpredictably.
For symptoms that are intermittent, a Holter monitor is the next step. It’s a small, portable device you wear for 24 to 48 hours while going about your normal routine, including sleep. It continuously records your heart rhythm so patterns that wouldn’t show up during a brief office visit can be caught.
When episodes are even less frequent, an event monitor extends the recording window to about 30 days. You wear the device continuously, but it only saves data when you press a button during symptoms. It captures the 30 seconds before you pressed and the 30 seconds after, giving your doctor a snapshot of exactly what your heart was doing when you felt something off. Newer implantable monitors can stay in place for years, useful for very rare episodes.
Symptoms That Signal a Problem
An abnormal heart rate by itself isn’t always dangerous. Many people live with occasional premature beats or mildly elevated resting rates without any health consequences. The combination of an unusual rate and symptoms is what raises the stakes.
Pay attention to palpitations (a fluttering, pounding, or racing sensation), dizziness or lightheadedness, unexplained fatigue, shortness of breath during activities that didn’t used to cause it, chest discomfort, and fainting or near-fainting. These suggest the heart isn’t circulating blood effectively, and the underlying rhythm needs evaluation. Atrial fibrillation and atrial flutter, in particular, carry stroke risk even when symptoms feel mild, which is why an irregular pulse is worth investigating regardless of how you feel in the moment.