Tachycardia is a resting heart rate above 100 beats per minute. That’s the standard threshold for adults, though the number shifts significantly for children, and context matters just as much as the raw count. A heart rate of 110 after climbing stairs is completely normal. A heart rate of 110 while sitting on the couch watching television is tachycardia.
The 100 BPM Threshold in Adults
A normal resting heart rate for adults falls between 60 and 100 beats per minute. Anything consistently above 100 at rest qualifies as tachycardia. “At rest” is the key phrase here. Your heart rate naturally rises during exercise, stress, or excitement, and that’s expected. Tachycardia becomes a concern when your heart races while you’re calm and still.
The 100 BPM line is a clinical convention, not a biological cliff edge. A resting rate of 98 isn’t perfectly healthy while 102 is dangerous. But the threshold gives doctors a consistent benchmark to flag hearts that are working harder than they should be.
Children Have Higher Normal Ranges
Kids’ hearts beat faster than adult hearts, so the 100 BPM rule doesn’t apply to them. A newborn’s normal heart rate ranges from about 120 to 170 beats per minute. By age one, the upper limit drops to around 150. At age six, it’s roughly 140. By the mid-teen years, heart rates settle into the adult range of 60 to 115 BPM. A heart rate of 130 in a toddler is perfectly normal, while the same rate in a teenager would be worth investigating.
Sinus Tachycardia: The Common, Usually Harmless Kind
The most common form of tachycardia is sinus tachycardia, where your heart’s natural pacemaker simply fires faster than usual in response to something your body is dealing with. Common triggers include fever, dehydration, stress, anxiety, caffeine, and certain medications. This type is your heart doing exactly what it’s supposed to do, just responding to a situation that demands more blood flow.
Sinus tachycardia typically resolves on its own once the trigger goes away. If you’re dehydrated, drinking fluids brings your rate down. If you have a fever, treating the underlying illness helps. Cutting back on caffeine, managing stress, and staying hydrated are the most practical steps for people who notice frequent episodes.
Types That Start in the Upper Heart Chambers
Supraventricular tachycardia (SVT) originates above the heart’s lower pumping chambers. Faulty electrical signals cause the heart to beat rapidly, sometimes reaching 250 BPM or higher during an episode. SVT tends to come on suddenly and can last anywhere from seconds to hours. It’s more common in younger people and is generally less dangerous than tachycardias that start in the lower chambers, though episodes can feel alarming.
Atrial fibrillation (often called AFib) is another upper-chamber tachycardia. Instead of beating in a coordinated rhythm, the upper chambers quiver chaotically, producing heart rates typically between 100 and 175 BPM. The distinguishing feature of AFib is an irregular pulse. Rather than a steady fast beat, you’ll feel an unpredictable rhythm, with some beats closer together and others farther apart.
Ventricular Tachycardia: The More Serious Type
When tachycardia originates in the heart’s lower chambers (the ventricles), it’s a more urgent situation. Ventricular tachycardia is more common in older adults and people with existing heart disease. Sustained episodes lasting more than 30 seconds can cause blood pressure to drop dramatically, leading to dizziness, breathlessness, or fainting.
The most dangerous progression is ventricular fibrillation, where the lower chambers quiver instead of pumping. This is a cardiac emergency. Blood pressure collapses, the pulse stops, and the person loses consciousness. This requires immediate CPR and emergency medical care.
POTS: Tachycardia Triggered by Standing Up
Postural orthostatic tachycardia syndrome (POTS) is a condition where your heart rate jumps dramatically when you move from lying down to standing. The diagnostic criteria require an increase of at least 30 BPM in adults (or 40 BPM in adolescents) within the first 10 minutes of standing. So someone whose heart rate goes from 70 lying down to 105 standing could meet the threshold. POTS often causes lightheadedness, brain fog, and fatigue, and it’s especially common in young women.
Exercise Heart Rate vs. Tachycardia
Your heart is designed to speed up during physical activity. A rough formula for estimating your maximum exercise heart rate is 220 minus your age. For a 40-year-old, that’s about 180 BPM. Hitting 150 or 160 during a hard workout is healthy, not tachycardia. The distinction is simple: if your heart rate is elevated because you’re exercising, it’s a normal physiological response. If it’s elevated while you’re resting or doing minimal activity, that’s when the 100 BPM threshold applies.
Symptoms That Signal a Problem
A fast heart rate doesn’t always produce noticeable symptoms. Some people discover tachycardia only when a doctor checks their pulse or they glance at a fitness tracker. When symptoms do appear, they can include a fluttering or pounding sensation in the chest, lightheadedness, feeling short of breath, or unusual fatigue.
Certain symptoms alongside a fast heart rate are red flags: chest pain or pressure, difficulty breathing, weakness, or fainting. These combinations suggest the heart isn’t pumping blood effectively and warrant immediate medical attention.
How Tachycardia Is Diagnosed
An electrocardiogram (EKG) is the primary tool for identifying tachycardia and determining its type. It records the electrical activity of your heart through sticky patches placed on your chest and takes only a few minutes. The pattern on the EKG tells doctors where in the heart the abnormal signals are originating, which is critical for choosing the right treatment approach.
Because tachycardia can come and go, a single EKG might miss it entirely. A Holter monitor solves this problem by continuously recording your heart rhythm for a day or more while you go about your normal routine. For episodes that happen infrequently, longer-term portable monitors can be worn for weeks.
If the underlying cause isn’t clear from these initial tests, doctors may use an echocardiogram (which uses sound waves to visualize how the heart is pumping), a tilt table test (to check if standing triggers an abnormal rate), or an electrophysiology study, where thin tubes are threaded through a blood vessel to map the heart’s electrical pathways from the inside. Heart imaging with CT or MRI scans is sometimes used to look for structural problems behind ventricular tachycardia.