Tachycardia: Prevention, Diagnosis and When to See a Doctor
A racing heart is normal during a sprint and alarming at rest on the sofa. For people who train, the line between healthy adaptation and a rhythm problem is not always obvious. Our editors explain what tachycardia means, which causes are common in active adults, how it is investigated in the UK and which symptoms should never be ignored.
What counts as tachycardia
In adults, tachycardia is conventionally defined as a resting heart rate above 100 beats per minute. The word describes a speed, not a diagnosis: a fast rate can be a perfectly appropriate response to exercise, fever or fright, or the sign of an electrical fault within the heart.
Trained people often have resting rates in the 40s or 50s, so a jump to 100 at rest represents a bigger relative change for them than for a sedentary person. Context therefore matters as much as the number shown on a watch.
Doctors separate two broad situations. In sinus tachycardia the heart's natural pacemaker is simply firing faster, usually because something is driving it. In arrhythmic tachycardia an abnormal circuit or focus takes over, producing a rate that may start and stop abruptly and does not match what the person is doing.
Wearables have made people far more aware of their pulse. That is useful, but optical sensors can misread during movement, and single readings out of context generate a lot of unnecessary worry. Repeated or symptomatic episodes are what deserve attention.
Types and common causes
Supraventricular tachycardias (SVT) arise above the ventricles. The most common forms in young, otherwise healthy people are AV nodal re-entrant tachycardia and accessory pathway tachycardias such as Wolff–Parkinson–White syndrome. They typically begin suddenly, feel like a fast regular pounding and may end just as abruptly.
Atrial fibrillation produces an irregular, often fast pulse. It becomes more common with age and is notably more frequent in long-term endurance athletes, particularly men in middle age. It matters because it raises the risk of stroke and can reduce exercise capacity.
Ventricular tachycardias originate in the lower chambers and are the most dangerous group. In athletes they may be linked to inherited conditions such as hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy or channelopathies, or to myocarditis after a viral illness.
Non-cardiac causes are common and treatable. They include:
- dehydration, fever and infection;
- anaemia and low iron stores;
- an overactive thyroid;
- anxiety and panic attacks;
- postural orthostatic tachycardia syndrome (PoTS), more common in young women;
- caffeine, nicotine, alcohol, decongestants and recreational drugs.
Triggers that matter for athletes
Stimulant-heavy pre-workout products are a frequent culprit. Large amounts of caffeine, sometimes combined with synephrine, yohimbine or undeclared stimulants, can push the resting rate up and provoke palpitations in susceptible people. The European Food Safety Authority considers single doses up to about 200 mg of caffeine safe for healthy adults; many products exceed that per scoop.
Performance-enhancing drugs are a more serious concern. Anabolic steroids, clenbuterol, thyroid hormone and amphetamine-type substances are associated with arrhythmias and structural heart changes. These are medical risks rather than performance tips, and they are one reason sports cardiologists ask directly about substance use.
Overreaching and poor recovery can also show up as a higher morning heart rate. Combined with illness, training through a fever is particularly risky because viral myocarditis can cause dangerous rhythms during exertion.
Finally, electrolyte shifts during very low-carbohydrate diets, rapid weight cuts or excessive sweating without replacement may contribute. The table summarises how different triggers tend to present.
| Trigger | Typical pattern | First step |
|---|---|---|
| High-stimulant supplements | Palpitations within hours of intake | Stop the product, note symptoms |
| Infection or fever | Raised rate at rest for days | Rest; no hard training until well |
| Dehydration or weight cut | Fast rate, dizziness on standing | Rehydrate, review the plan |
| Possible SVT | Sudden start and stop, regular | GP review and ECG |
| Doping substances | Persistent or irregular fast rate | Medical assessment, honest history |
How tachycardia is diagnosed
The starting point is a detailed history: when episodes begin, how long they last, whether the rhythm feels regular, what the person was doing and whether there was dizziness, breathlessness or chest pain. Family history of sudden death under 40 is especially important.
A 12-lead ECG is the basic test. If it can be recorded during an episode, it often gives the answer immediately. Between episodes it may still show clues such as pre-excitation or features of cardiomyopathy. ECGs in athletes should be read using athlete-specific criteria, because training causes changes that would look abnormal in untrained people.
When symptoms are intermittent, ambulatory monitoring is used: a 24-hour or longer Holter monitor, an event recorder or, for rare episodes, an implantable loop recorder. Smartphone ECG devices can be helpful for capturing an episode to show the doctor.
Further tests depend on findings. Blood tests check thyroid function, full blood count and electrolytes. An echocardiogram looks at heart structure, an exercise test examines how the rhythm behaves under load, and cardiac MRI or an electrophysiology study are used in specialist settings.
When to seek help and how to lower the risk
Call 999 if a fast heart rate comes with chest pain, fainting, severe breathlessness or confusion, or if someone collapses during exercise. In that situation, starting CPR and using a defibrillator saves lives; every athlete and coach benefits from knowing where the nearest one is.
Contact NHS 111 or your GP promptly if palpitations recur, last more than a few minutes, start and stop suddenly, or happen at rest without an obvious reason. Anyone with a family history of sudden cardiac death or inherited heart disease should mention it and ask about screening.
Prevention focuses on the modifiable triggers. Keep caffeine within sensible limits and read labels of pre-workout products carefully. Avoid training hard with a fever or during the first days of a viral illness, return gradually afterwards and pay attention to sleep and hydration.
Above all, do not use prescription drugs or doping substances to control weight or boost performance. Some, such as thyroid hormone and clenbuterol, directly drive the heart rate and can provoke dangerous arrhythmias even in young people.
Conclusions of the editorial team
Tachycardia is a description of speed with many possible causes, from a strong espresso to an inherited heart condition. For active people, context and accompanying symptoms are the key to telling them apart.
Most episodes have an identifiable trigger, and diagnosis in the UK follows a clear path from history and ECG to monitoring and specialist tests when needed.
Fainting, chest pain or collapse during exercise always need urgent assessment, and recurring palpitations deserve a GP appointment rather than repeated checks on a smartwatch.
You may also find it useful to read our articles on caffeine safety in pre-workout products, on returning to training after a viral illness, and on pre-participation heart screening for athletes.
References
- Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia. Eur Heart J. 2020;41(5):655–720.
- Hindricks G, Potpara T, Dagres N, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation. Eur Heart J. 2021;42(5):373–498.
- Pelliccia A, Sharma S, Gati S, et al. 2020 ESC Guidelines on sports cardiology and exercise in patients with cardiovascular disease. Eur Heart J. 2021;42(1):17–96.
- Drezner JA, Sharma S, Baggish A, et al. International criteria for electrocardiographic interpretation in athletes. Br J Sports Med. 2017;51(9):704–731.
- Sheldon RS, Grubb BP, Olshansky B, et al. 2015 Heart Rhythm Society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope. Heart Rhythm. 2015;12(6):e41–e63.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the safety of caffeine. EFSA J. 2015;13(5):4102.
