What is Supraventricular Tachycardia (SVT)?
SVT is when your heart suddenly starts racing very fast (over 100 beats per minute) because of an electrical problem in the upper chambers of your heart or the wiring that connects them to the lower chambers. 1
How Your Heart Normally Works
Think of your heart like a house with an electrical system. Normally, electricity starts in the attic (upper chambers called atria), travels through a junction box (called the AV node), and then powers the basement (lower chambers called ventricles). This happens in an organized way, about 60-100 times per minute.
What Goes Wrong in SVT
In SVT, the electrical system develops a short circuit or an extra wire that shouldn't be there. This causes the electricity to loop around repeatedly or fire too quickly, making your heart race—sometimes 150-250 beats per minute or even faster. 2, 1
The key point is that this electrical problem happens "above" the main pumping chambers (that's what "supraventricular" means—"supra" = above, "ventricular" = the ventricles). 1
What It Feels Like
When SVT happens, you'll typically notice:
- Sudden onset: Your heart abruptly starts pounding, like flipping a light switch 1, 3
- Palpitations: Feeling your heart racing or fluttering in your chest (86% of people) 4
- Chest discomfort or pressure (47% of people) 4
- Shortness of breath (38% of people) 4
- Lightheadedness or dizziness 2, 5
- Anxiety (because it feels scary when your heart suddenly races) 2
- Sudden stop: Just as abruptly as it started, it stops 1, 3
Common Types (The Three Main Culprits)
There are three main types of short circuits that cause SVT:
AVNRT (50-60% of cases): The junction box (AV node) has two pathways instead of one, and electricity loops between them like a dog chasing its tail 3
AVRT (25-30% of cases): You were born with an extra wire connecting the upper and lower chambers (called an accessory pathway), and electricity travels in a circle using both the normal pathway and this extra wire 3
Atrial Tachycardia (10% of cases): A spot in the upper chamber starts firing electrical signals too rapidly on its own 3
Who Gets It
- About 2-3 people per 1,000 in the general population have SVT 2, 1
- Women are twice as likely to develop it compared to men 2, 1
- Risk increases with age: People over 65 have 5 times higher risk than younger people 2, 1
- Most people have structurally normal hearts—meaning the heart muscle itself is fine, just the electrical wiring is problematic 6
Is It Dangerous?
Unlike heart attacks or dangerous rhythms from the lower chambers, SVT is rarely life-threatening. 2 However, if left untreated for long periods, it can cause:
- Heart failure (the heart gets tired from racing constantly) 2
- Tachycardia-induced cardiomyopathy (weakening of the heart muscle from prolonged fast rates, though this is rare at only 1% of cases) 2, 4
The Bottom Line
SVT is like having a glitch in your heart's electrical system that makes it suddenly race very fast and then stop just as suddenly. While it feels frightening and uncomfortable, it's usually not dangerous and is highly treatable. Most people with SVT have otherwise normal hearts—it's just the wiring that needs fixing.