Tachycardia is a resting heart rate above 100 beats per minute in adults. A normal resting heart rate falls between 60 and 100 beats per minute, so anything consistently above that upper limit qualifies. That said, context matters: your heart rate naturally rises during exercise, stress, or a fever, and those temporary spikes are not the same as a sustained fast heart rate at rest.
Why 100 BPM Is the Cutoff
The 100 BPM threshold applies to adults sitting or lying still. If you check your pulse after climbing stairs or during an argument, a reading above 100 is expected and not a sign of tachycardia. The key word is “resting.” To get an accurate reading, sit quietly for at least five minutes before measuring.
Children have naturally faster heart rates than adults, and what counts as “too fast” depends on age. A newborn’s median heart rate is around 127 beats per minute and peaks near 145 at about one month old, then gradually declines. By age two, the median drops to about 113. For children between 2 and 10, heart rates above roughly 140 are generally considered elevated. As kids move through adolescence, their resting rates approach adult ranges.
Types of Tachycardia
Not all fast heart rates work the same way. The type depends on where in the heart the abnormal electrical signals originate.
Sinus tachycardia is the most straightforward type. Your heart’s natural pacemaker (the sinus node) simply fires faster than usual. This is the kind you experience during exercise, anxiety, pain, or a high fever. It’s usually a response to something rather than a problem with the heart itself.
Supraventricular tachycardia (SVT) involves abnormal electrical circuits in the upper chambers of the heart. During an SVT episode, the heart typically beats between 150 and 220 times per minute, sometimes faster. Episodes often start and stop suddenly. The most common subtype, called AVNRT, involves a short circuit near the connection point between the upper and lower chambers.
Ventricular tachycardia (VT) originates in the lower chambers. This type is more concerning because the lower chambers do most of the work pumping blood to your body. VT can sometimes be a medical emergency, especially if it lasts more than a few seconds or causes symptoms like fainting.
Common Causes
A fast heart rate is a symptom, not a diagnosis on its own. Finding the underlying cause is what determines whether it needs treatment.
The most common triggers are everyday and temporary: physical activity, emotional stress, pain, anxiety, caffeine, and dehydration. Fever raises heart rate reliably, with the heart beating roughly 10 extra beats per minute for every degree Fahrenheit above normal. These are all examples of sinus tachycardia, where the heart is responding appropriately to a demand.
Medications and substances can also push heart rate up. Stimulants like caffeine, amphetamines, and cocaine are well-known culprits. But plenty of common medications have the same effect, including asthma inhalers, decongestants containing pseudoephedrine, thyroid hormone replacements, certain antidepressants, and antihistamines. If your resting heart rate is consistently elevated, a medication review is a reasonable starting point.
More serious causes include infections severe enough to trigger a systemic inflammatory response, heart muscle inflammation (myocarditis), coronary artery disease, and fluid buildup around the heart. Anemia and an overactive thyroid are other medical conditions that commonly produce a sustained fast heart rate.
Postural Tachycardia Syndrome (POTS)
Some people experience a dramatic heart rate increase simply from standing up. POTS is diagnosed when your heart rate jumps by 30 or more beats per minute (or 40 or more in adolescents aged 12 to 19) within 10 minutes of standing, and this pattern persists for at least three months. The heart rate itself may or may not cross the 100 BPM line while seated, but it spikes significantly with posture changes. Common accompanying symptoms include dizziness, brain fog, fatigue, and near-fainting.
What Tachycardia Feels Like
Some people with a resting heart rate above 100 feel nothing unusual. Others notice distinct symptoms. The most common is palpitations: a racing, pounding, or fluttering sensation in the chest. You might also experience lightheadedness, shortness of breath, chest discomfort, or in more severe cases, fainting. SVT episodes tend to produce especially noticeable symptoms because the heart rate is so much higher, often starting abruptly and creating a sensation that something is clearly wrong.
Symptoms that warrant calling emergency services include rapid palpitations combined with chest pain, severe shortness of breath, or dizziness that makes you feel like you might pass out. These combinations can indicate that the heart is not pumping blood effectively.
How Tachycardia Is Diagnosed
The starting point is almost always an electrocardiogram (ECG), a quick, painless test where sensors are placed on your chest to record the heart’s electrical activity. An ECG can often identify the type of tachycardia and where the abnormal signals are coming from. The catch is that it only captures what’s happening in that moment, so if your episodes come and go, a standard ECG might look completely normal.
For intermittent symptoms, a Holter monitor is a portable device you wear for a day or more while going about your routine. It continuously records your heart rhythm and catches episodes that a single ECG would miss. An echocardiogram, which uses ultrasound to create images of the heart, checks whether the structure and pumping function look normal.
When these initial tests point toward a specific arrhythmia but more detail is needed, an electrophysiology (EP) study can map the heart’s electrical pathways precisely. During this test, thin flexible tubes are threaded through a blood vessel (usually in the groin) to the heart. This is typically reserved for cases where a procedure to correct the arrhythmia is being considered. For ventricular tachycardia specifically, a cardiac MRI or CT scan may be used to look for structural problems in the heart muscle that could be driving the abnormal rhythm.
What Affects Your Baseline Heart Rate
Your normal resting heart rate is shaped by fitness level, age, medications, and genetics. Well-trained endurance athletes can have resting rates in the 40s or 50s, while a sedentary person might sit comfortably in the 80s or 90s. Both can be perfectly healthy. Beta-blockers and certain calcium channel blockers lower resting heart rate, while the stimulants and medications listed earlier raise it.
A single reading above 100 after a cup of coffee or a stressful phone call is not tachycardia in any clinical sense. Persistent elevation, or episodes of very rapid heart rates (150 and above) that come on without an obvious trigger, is what warrants investigation. If you’re tracking your heart rate with a smartwatch or fitness band, look at patterns over days and weeks rather than reacting to any single number.