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Dr. Alessandro Giardini
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When a teenager says their heart is racing, the description is usually clear enough to work with. When a baby or toddler has a fast heart rhythm, there are no words at all. That is what makes this age group so challenging for parents. Many families have a sense that something is wrong before anyone has identified a specific symptom. They know their child. They can tell the baby is not quite themselves, that something feels off. That instinct is worth taking seriously, and it is something I hear repeatedly in clinic from parents of very young children.
The sensation of palpitations depends on self-awareness and the ability to communicate an internal experience. A two-year-old cannot say their heart feels like it is fluttering. A six-month-old cannot point to their chest and describe a racing feeling. What they can do is show that something is wrong through behaviour and physical signs, and parents who know their child well are often remarkably accurate in identifying that a change has occurred.
The signs in infants can be subtle and easy to attribute to other causes. Poor feeding is one of the earliest. A baby who normally feeds well and suddenly refuses, takes much less than usual, or becomes very breathless during a feed may be showing signs of a fast heart rhythm. Pallor, a greyish skin tone, unusual fussiness, and rapid breathing at rest are all relevant. In some cases, a parent notices the chest wall moving faster than usual, or feels the heart beating very fast when they hold the baby against their chest.
Toddlers aged one to three sometimes grab at their chest or point to it without being able to explain why. Sudden pallor, refusing to play, and sitting down abruptly during activity can all reflect episodes where the heart has temporarily moved into a fast rhythm.
Supraventricular tachycardia is the most common significant arrhythmia in infants and young children. SVT involves a sudden switch to a very fast heart rate, often between 200 and 300 beats per minute in babies, driven by an abnormal electrical pathway in the heart.
The condition can be present from birth. In some babies, episodes begin in the newborn period or even before birth, detected on a routine antenatal scan showing an unusually fast foetal heart rate. Others experience their first episode in infancy or early childhood.
One important feature of SVT in infants is that episodes can persist for hours before being recognised. A baby's heart is reasonably tolerant of fast rates for a period, which means an episode may have been going on for some time before it becomes clinically obvious. This is why recognising the early behavioural signs matters. A prolonged undetected fast heart rhythm can eventually affect the heart's pumping function.
Not every fast heart rate in a baby is SVT. Fever, pain, crying, and agitation all raise the heart rate physiologically. Context is everything. A calm, afebrile baby with a persistently fast, regular heart rate and pallor is a different situation from a distressed, crying baby with a raised rate during active discomfort.
A single brief episode of unusual behaviour in an otherwise well baby, who quickly returns to normal, is often benign. Isolated moments of fussiness, brief pallor, or a slightly fast heartbeat felt through the chest during a normal feed do not necessarily signal a problem.
Seek urgent medical attention if your baby or toddler appears pale or grey, is breathing unusually fast at rest, refuses to feed, is unusually limp or unresponsive, or if you can feel or see the heart beating very fast through the chest wall and the episode is not resolving within a few minutes. These are signs that need immediate assessment. Do not wait to see if the episode settles on its own if your child looks genuinely unwell.
For episodes that have resolved by the time you see a doctor, a clear description of exactly what you observed, how long it lasted, and how the child looked and behaved will be some of the most useful information a cardiologist receives. I ask parents these questions in detail at every initial consultation for this age group, because the history is often the most important part of the whole assessment.
An ECG is usually the starting point. It is quick, painless, and gives immediate information about the heart's electrical activity. In very young children it can take two people, one to support the child comfortably and one to apply the electrodes, but the test itself takes only seconds.
If episodes are infrequent and have not been captured on ECG, ambulatory monitoring over 24 to 48 hours may be recommended. Modern patch monitors are small and can be tolerated even by toddlers for short periods. An echocardiogram is frequently performed as well, because it is important to understand the heart's structure and function alongside its rhythm.
In babies where SVT is diagnosed, the approach to treatment is tailored to the child's age, the frequency and duration of episodes, and whether there is an underlying structural heart issue. I discuss the full range of options with families in the context of their individual child, covering medication to prevent recurrence and vagal techniques for older toddlers.
Normal heart rates in infants range from approximately 100 to 160 beats per minute, and rates up to 180 can be seen during crying or active feeding. Rates consistently above 200 in a calm, afebrile baby are outside the normal range and warrant assessment.
Many babies who develop SVT in the first year of life do improve, with episodes becoming less frequent or stopping altogether as the child grows. There is, however, a meaningful chance of recurrence in later childhood or adolescence. Ongoing follow-up after a diagnosis in infancy is important.
Yes, it is worth describing the episode to your GP or paediatrician, particularly if it was unlike your baby's usual behaviour and resolved suddenly rather than gradually. An ECG and review are reasonable first steps.
Most SVT in babies is not life-threatening, particularly when identified and managed appropriately. Prolonged episodes lasting several hours without recognition or treatment can affect the heart's pumping function, which is why early identification matters. Most affected children do very well.
Sometimes, yes. An unusually fast foetal heart rate detected on ultrasound during pregnancy can indicate SVT in the unborn baby. This situation is managed in conjunction with foetal medicine specialists and paediatric cardiologists before delivery.
Author: Dr. Alessandro Giardini, MD, PhD
Written 22/05/2026