A resting heart rate above 100 beats per minute in an adult is considered high, a condition called tachycardia. Normal resting heart rate for anyone 13 and older falls between 60 and 100 bpm. A high reading doesn’t always signal a problem. In many cases, it’s a temporary response to something your body is dealing with, from stress to dehydration to your morning coffee. But a persistently elevated heart rate can also point to an underlying condition worth investigating.
What Counts as “High” at Different Ages
Heart rate norms shift dramatically from birth through adulthood. A newborn’s resting heart rate can be as high as 205 bpm and still be perfectly normal. Infants up to one year old range from 100 to 180 bpm. Toddlers settle into 98 to 140, preschoolers into 80 to 120, and school-age children into 75 to 118. By adolescence, the adult range of 60 to 100 bpm kicks in and stays there for life.
If you’re checking a child’s heart rate against adult standards, you’ll almost certainly think something is wrong when it isn’t. Always compare to the age-appropriate range. And keep in mind that these numbers apply when you’re awake and at rest. Sleep typically lowers your rate, while any physical activity raises it.
Everyday Reasons Your Heart Rate Spikes
The most common causes of a temporarily high heart rate aren’t medical conditions at all. They’re situations your body responds to by speeding up the pump.
Stress and anxiety. When your brain perceives a threat, even a non-physical one like a work deadline or an argument, it triggers a hormonal cascade. Your adrenal glands release adrenaline, which directly increases your heart rate, raises blood pressure, and floods your muscles with extra energy. This is the classic fight-or-flight response. It’s completely normal in short bursts, but chronic stress keeps adrenaline and cortisol elevated, which can keep your heart rate higher than it should be for hours or days at a time.
Caffeine and nicotine. Caffeine promotes the release of noradrenaline, a chemical cousin of adrenaline, which speeds up the heart. Most people tolerate moderate amounts fine, but sensitivity varies widely. If you notice your heart racing after coffee, energy drinks, or pre-workout supplements, you’re feeling that noradrenaline surge. Nicotine has a similar stimulant effect on heart rate.
Dehydration. When your blood volume drops because you haven’t had enough fluids, or because you’ve lost fluids through sweating, vomiting, or diarrhea, your heart compensates by beating faster to maintain adequate blood flow. This is one of the most overlooked causes of an elevated resting heart rate, especially in warm weather or after exercise.
Fever and illness. Your metabolic rate increases when you’re fighting an infection, and your heart rate rises along with it. A rate in the low 100s during a fever is typical and usually resolves as the illness passes.
Medical Conditions That Raise Heart Rate
When a high heart rate persists without an obvious trigger, it may reflect an underlying health issue.
Electrolyte imbalances. Minerals like sodium, potassium, and calcium play a direct role in regulating your heart’s electrical signals. When these levels fall out of balance, whether from prolonged vomiting, heavy sweating, certain medications, or kidney problems, the result can be a fast or irregular heartbeat. Potassium is especially important for heart, nerve, and muscle function, and even mild deficiencies can affect your rhythm.
Thyroid overactivity. An overactive thyroid floods your body with hormones that lower resistance in your blood vessels while simultaneously increasing your resting heart rate. These hormones alter the behavior of sodium, potassium, and calcium channels in heart cells, essentially rewiring your heart’s electrical activity to run faster. If a high heart rate comes with unexplained weight loss, heat intolerance, or tremors, thyroid function is one of the first things worth checking.
Anemia. When your blood carries fewer red blood cells or less oxygen than normal, your heart beats faster to compensate for the shortfall. This is why people with iron deficiency often notice their heart pounding during activities that previously felt easy.
Types of Abnormal Heart Rhythms
Not all fast heart rates feel or behave the same way. Two of the most common rhythm disorders sit at opposite ends of the spectrum.
Atrial fibrillation is a chaotic, irregular rhythm where the heart’s upper chambers fire errant electrical signals more than 300 times per minute, causing them to quiver instead of contracting properly. The lower chambers beat irregularly too, which is why people with atrial fibrillation often describe their heartbeat as “fluttering” or “skipping.” It primarily affects people 65 and older.
Supraventricular tachycardia, or SVT, is different. The rhythm is fast but regular, sometimes reaching 200 beats per minute. It can strike at any age, even in children, though the average age of diagnosis is 45. Episodes often start and stop abruptly, which distinguishes them from the more persistent irregularity of atrial fibrillation.
Both conditions originate from electrical misfiring above the heart’s lower chambers, but the pattern of that misfiring is what separates them. A wearable heart monitor recording your rhythm over two to four weeks is one of the main tools used to tell them apart. Some smartwatches that record brief electrical snapshots of heart activity can also help capture episodes that come and go unpredictably.
How Your Heart Rate During Exercise Compares
A high heart rate during physical activity is expected and healthy. The question is how high. A widely used formula from the Norwegian University of Science and Technology estimates your maximum heart rate as 211 minus 0.64 times your age. For a 40-year-old, that’s roughly 185 bpm. For a 60-year-old, about 173.
These numbers represent the ceiling, not the target. Most moderate exercise keeps you at 50 to 70 percent of your maximum, while vigorous exercise pushes into the 70 to 85 percent range. If your heart rate regularly exceeds your estimated max during light activity, or takes a long time to come back down afterward, that’s worth paying attention to.
Symptoms That Need Immediate Attention
A fast heart rate on its own, especially if you can trace it to exercise, caffeine, or stress, is usually not dangerous. But certain combinations of symptoms change the picture. Rapid heart palpitations paired with dizziness, chest pain, or severe shortness of breath constitute an emergency. In severe cases, tachycardia can cause loss of consciousness. If you experience any of these, call emergency services immediately.
Less urgent but still worth investigating: a resting heart rate that stays above 100 bpm for days without a clear reason, episodes where your heart suddenly races and then stops on its own, or a fast heartbeat accompanied by unusual fatigue or lightheadedness.
How a High Heart Rate Gets Evaluated
The most basic test is an electrocardiogram, a quick, painless recording of your heart’s electrical activity using sticky patches placed on your chest. It captures what your heart is doing in that moment, which is useful if the fast rate is happening during the test but less helpful for episodes that come and go.
For intermittent symptoms, a Holter monitor (a small wearable device with sensors) records your heart’s rhythm continuously for a day or more while you go about your normal routine. An echocardiogram uses sound waves to create images of your heart in motion, showing how blood flows through the chambers and valves. These three tests cover the majority of evaluations.
If the cause remains unclear, more specialized options exist. An electrophysiology study threads thin flexible tubes through a blood vessel into the heart to map exactly where abnormal electrical signals originate. Cardiac MRI or CT scans provide detailed structural images when a problem with the heart muscle itself is suspected. Your doctor chooses among these based on which type of rhythm disorder the initial tests suggest.