A high heart rate, medically called tachycardia, is a resting heart rate above 100 beats per minute (bpm) in adults. The normal resting range for anyone 13 and older is 60 to 100 bpm. A heart rate that stays elevated at rest, or spikes without an obvious reason like exercise, can signal anything from dehydration to an underlying medical condition.
Normal Resting Heart Rate by Age
What counts as “high” depends heavily on age. Babies and young children have naturally faster hearts. A newborn’s resting rate can be as high as 205 bpm and still be considered normal, while a toddler’s range is roughly 98 to 140 bpm. By adolescence, the range settles into the adult standard of 60 to 100 bpm and stays there for the rest of life.
Fitness level shifts the picture, too. A study of over 1,500 collegiate athletes found average resting heart rates around 63 bpm, with some endurance runners sitting as low as 35 to 38 bpm. A well-trained heart pumps more blood per beat, so it doesn’t need to beat as often. If you’re sedentary and your resting rate consistently sits in the upper 90s, that’s technically normal but may be worth paying attention to. Sleep also matters: your resting rate naturally drops while you’re asleep and rises when you’re active or awake.
Common Causes of an Elevated Heart Rate
Many everyday factors push your heart rate above its baseline without any serious condition being involved. Caffeine, nicotine, stress, anxiety, poor sleep, and fever all speed up your heart temporarily. These triggers activate your body’s fight-or-flight response, releasing stress hormones that tell the heart to pump faster.
Dehydration is one of the most underrecognized causes. When you’re low on fluids, your blood volume drops, which means your heart has less blood available to pump with each beat. It compensates by beating more frequently. Dehydration also disrupts electrolyte balance, and electrolytes are essential for the electrical signals that keep your heart rhythm steady. An imbalance can provoke irregular rhythms and palpitations on top of a faster rate.
Certain medications, including decongestants, some asthma inhalers, and stimulant medications, can raise heart rate as a side effect.
Medical Conditions That Cause Tachycardia
When a high heart rate is persistent rather than temporary, a medical condition is often involved. Some of the most common include:
- Anemia: With fewer red blood cells carrying oxygen, the heart beats faster to deliver enough oxygen to tissues.
- Overactive thyroid (hyperthyroidism): Excess thyroid hormone speeds up metabolism across the body, including heart rate.
- POTS (postural orthostatic tachycardia syndrome): Heart rate jumps 30 bpm or more within 10 minutes of standing up. It’s more common in women and often develops after a viral illness, pregnancy, surgery, or head injury. People with autoimmune conditions like lupus or celiac disease are also at higher risk.
- Heart rhythm disorders (arrhythmias): Faulty electrical signaling within the heart itself can drive rapid, sustained, or irregular beats independent of outside triggers.
What a High Heart Rate Feels Like
You might notice your heart pounding, fluttering, or racing in your chest. These sensations, called palpitations, are the most common symptom. They often show up during periods of stress, physical exertion, or sometimes when you’re simply resting or lying down at night. Some people feel them in the neck or throat rather than the chest.
Beyond palpitations, a sustained high heart rate can cause lightheadedness, shortness of breath, fatigue, and a general sense that something feels off. Brief episodes lasting a few seconds often pass without harm. Episodes that last more than a few seconds, or that happen repeatedly, deserve medical evaluation.
When a High Heart Rate Is Dangerous
Most episodes of tachycardia are uncomfortable but not immediately life-threatening. However, certain warning signs indicate an emergency. Seek immediate care if a racing heart is accompanied by chest pain lasting more than a few minutes, fainting or near-fainting, or severe shortness of breath.
The most dangerous form of tachycardia is ventricular fibrillation, where the heart’s lower chambers quiver chaotically instead of pumping blood. Blood pressure drops dramatically, breathing and pulse stop, and the person essentially goes into cardiac arrest. This requires emergency treatment within minutes to survive. While rare, it’s the reason persistent or severe tachycardia should never be ignored.
How Doctors Evaluate a High Heart Rate
The starting point is usually an electrocardiogram (ECG or EKG), a quick, painless test where sensors placed on your chest record the heart’s electrical activity. It reveals whether the heart is beating too fast, too slow, or irregularly, and can identify certain rhythm disorders on the spot.
If the ECG doesn’t capture the problem because your heart rate happens to be normal during the test, you may wear a Holter monitor. This small, portable device records your heartbeat continuously for a day or more while you go about your daily routine, catching episodes that come and go.
Depending on results, further testing might include an echocardiogram (ultrasound images of the heart in motion), stress testing on a treadmill, or a tilt table test to evaluate whether a fast heart rate causes fainting when you change position. For more complex cases, an electrophysiology study threads thin, flexible tubes through a blood vessel to map exactly where abnormal electrical signals originate inside the heart.
Heart Rate During Exercise
A high heart rate during physical activity is expected and healthy. What matters is whether it stays within an appropriate range for your age. The simplest way to estimate your maximum heart rate is with the formula 208 minus 0.7 times your age, which research has shown to be more accurate than the older “220 minus age” rule. For a 40-year-old, that works out to about 180 bpm.
The American Heart Association defines moderate-intensity exercise as 50 to 70 percent of your maximum heart rate, and vigorous exercise as 70 to 85 percent. For that same 40-year-old, moderate intensity means roughly 90 to 126 bpm, and vigorous means 126 to 153 bpm. Exceeding your maximum heart rate during exercise, or finding that your heart rate stays elevated long after you stop, can be a sign that something else is going on.
Lowering a High Resting Heart Rate
If your resting heart rate runs high but no underlying condition is found, lifestyle changes can bring it down over time. Regular aerobic exercise is the single most effective tool. As your heart becomes stronger, it pumps more blood per beat and doesn’t need to beat as often at rest. Even moderate activity like brisk walking, done consistently, makes a measurable difference over weeks to months.
Staying well-hydrated, cutting back on caffeine, managing stress, and getting consistent sleep all help. For people whose tachycardia is driven by a medical condition, treating the root cause (correcting anemia, managing thyroid levels, addressing an arrhythmia) typically brings the heart rate back to normal range.