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At Cardiology Center Zacharias Kounnis, a leading cardiology center in Limassol, we often see patients who experience a rapid heartbeat that doesn’t seem to match their activity level. This can be caused by two commonly misunderstood conditions: Inappropriate Sinus Tachycardia (IST) and Postural Orthostatic Tachycardia Syndrome (POTS). Though different in their mechanisms, both conditions can significantly impact daily life—and both can be managed effectively with the right diagnosis and care.
IST is a condition where the sinus node (the natural pacemaker of the heart) sends signals too frequently, leading to an elevated heart rate at rest or with minimal activity. Unlike normal physiological responses to exercise or stress, IST has no obvious trigger. The heart may beat too fast even while sitting or lying down.
POTS is a type of dysautonomia, which affects the autonomic nervous system. It is defined by a significant increase in heart rate upon standing, without a corresponding drop in blood pressure. It mostly affects young adults, especially women, and can be misdiagnosed as anxiety or panic disorder.
Both IST and POTS require a careful and specialized approach to diagnosis and management, which is where the expertise of the best cardiology center in Cyprus comes in.
While the exact cause of IST and POTS isn’t always clear, several factors may contribute:
At Cardiology Center Zacharias Kounnis, we utilize advanced diagnostic tools such as Holter monitors, tilt-table testing, and ECGs to ensure accurate assessment.
Treatment for IST and POTS is highly individualized and often includes a combination of:
As a top-rated cardiology center in Limassol, we provide comprehensive follow-up and patient education to help our patients regain control of their lives.
When it comes to complex conditions like IST and POTS, experience matters. At Cardiology Center Zacharias Kounnis, recognized as the best cardiology center in Cyprus, our team of expert cardiologists offers:
Inappropriate sinus tachycardia, or IST, involves an unusually fast sinus heart rate that may occur at rest or with limited physical activity. POTS is characterised by an excessive increase in heart rate after moving into an upright position and is commonly associated with symptoms such as dizziness, weakness, palpitations and exercise intolerance.
Some symptoms can resemble anxiety, including a racing heartbeat, sweating, dizziness and breathlessness. However, IST and POTS are physical conditions that require proper medical evaluation. Symptoms should not automatically be attributed to anxiety without appropriate assessment.
Diagnosis may involve a detailed medical history, physical examination, heart-rate and blood-pressure measurements, an ECG, blood tests, Holter monitoring and testing of the heart’s response to standing. Additional examinations may be recommended depending on the patient’s symptoms.
The severity and impact vary considerably between patients. These conditions are not usually treated in exactly the same way, so an accurate diagnosis is important. New chest pain, fainting, severe breathlessness or rapidly worsening symptoms require prompt medical assessment.
A fast heartbeat can have several possible causes, including dehydration, anaemia, thyroid disorders, medication effects and other rhythm conditions. A personalised evaluation is necessary before symptoms can be classified as IST or POTS.
Depending on your symptoms, assessment may include Holter rhythm monitoring, an ECG and rhythm recording and further arrhythmia diagnosis and treatment.
You can also read our guide explaining when heart palpitations require cardiology evaluation.
Schedule an appointment at Cardiology Center Zacharias Kounnis for a personalised heart-rhythm assessment in Limassol.
Prepared by: Cardiology Center Zacharias Kounnis Medical Content Team
Medically reviewed by: Dr Zacharias Kounnis, Cardiologist
Last medically reviewed: 20 September 2026
Last updated: 20 September 2026
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