The basics | SVT | Cardiology Made Clear with Dr. Freeman

← Supraventricular tachycardia (SVT): the short explanation

All 6 sections, including text and pictures · 28 pages

What should I do now?

Call 911

Call 911 if racing occurs with chest pressure, severe trouble breathing, fainting, or severe weakness or dizziness. Do not drive yourself.

Contact your care team

Contact your care team if episodes are new, more frequent, longer, or interfere with daily life. Follow your personal plan when an episode will not stop.

Keep your care plan

Keep your treatment and follow-up plan. Bring questions, readings, and your medication list.

Take-home summary →One-page PDF

01 / UNDERSTAND SVT

What is SVT?

Supraventricular tachycardia, or SVT, is a group of abnormal heart rhythms that make the heart beat faster than it should. “Supraventricular” means coming from the heart’s upper chambers. “Tachycardia” means a fast heart rate.

Many common SVTs cause episodes of a rapid, regular heartbeat that start and stop suddenly—almost like flipping a switch. An episode may occur while you are resting or active.

How does the heart normally beat?

Labeled cutaway heart showing the SA node, AV node, bundle of His, right and left bundle branches, Purkinje fibers, and left atrial appendage. — Follow one normal heartbeat
**SA node → Atria → AV node → Ventricles**
**The SA node starts the signal.** The heart’s natural pacemaker in the right upper chamber begins each normal sinus beat.
**The signal spreads through both atria.** The upper chambers contract, moving blood into the ventricles.
**The AV node briefly delays the signal.** This pause gives the ventricles time to finish filling.
**The signal activates the ventricles.** It travels through the bundle of His, right and left bundle branches, and Purkinje fibers. The lower chambers contract, pumping blood to the lungs and body.
**The atria contract first; the ventricles follow.** This organized sequence produces a coordinated heartbeat.
NHLBI: How the heart beats MedlinePlus: Cardiac conduction system

Sinus rhythm

Normal sinus rhythm: an organized electrical signal coordinates the heartbeat. The EKG shows one P wave before each QRS complex and regular spacing between beats. Illustrative tracing; timing and voltage are not calibrated.

What changes during SVT?

In common types of SVT, an electrical signal becomes trapped in a repeating loop, or an abnormal electrical source sends signals faster than the sinus node. These signals take over the rhythm and drive the heart too quickly.

SVT is an electrical problem. Having SVT does not necessarily mean you have blocked arteries or a weak heart.

There are multiple types of SVT

There are several types of SVT. Here, we’ll focus on three of the main types: AVNRT, AVRT, and atrial tachycardia. Each involves a different electrical pathway or source. Understanding which type you have helps explain why episodes happen and how they can be treated.

Type 1: AVNRT—a loop near the AV node

AV nodal reentrant tachycardia, or AVNRT, occurs when two electrical pathways in or near the AV node allow a signal to circle repeatedly.

These are often called the fast pathway and the slow pathway. Under the right conditions, a premature heartbeat can start a loop that travels down one pathway and back up the other. Each trip around the loop triggers another heartbeat.

Magnified AV nodal region showing typical AVNRT: orange arrows travel down the slow pathway, blue arrows return up the fast pathway, and a separate downward signal travels toward the ventricles. — **Fast and regular:** The tall, narrow QRS spikes are evenly spaced. In typical AVNRT, the upper and lower chambers activate almost together, so the P waves are often hidden within the QRS complexes. This is an illustrative example, not a patient recording; timing and voltage are not calibrated. A clinician reviews the EKG to distinguish AVNRT from other fast rhythms.

Type 2: AVRT—a loop using an extra connection

AV reentrant tachycardia, or AVRT, uses an extra electrical connection between the atria and ventricles, called an accessory pathway.

The signal can travel down the normal electrical route and return through the extra connection, creating a repeating loop.

Some accessory pathways are associated with Wolff-Parkinson-White, or WPW. Others do not show up on an EKG taken during normal rhythm.

Labeled cutaway heart showing orthodromic AVRT with downward normal AV conduction, ventricular activation, and upward return through a left lateral accessory pathway at the mitral valve junction. — **Fast and regular:** The narrow QRS spikes are evenly spaced. The small downward waves just after them represent **retrograde P waves**—the atria being activated as the signal returns up the accessory pathway. These P waves are not always easy to see. This is an illustrative example, not a patient recording; timing and voltage are not calibrated. The strip alone does not identify where the accessory pathway is located.

Type 3: Atrial tachycardia—an abnormal electrical source

In focal atrial tachycardia, a small area in an atrium sends electrical signals faster than the sinus node. This area temporarily takes over as the rhythm’s driver.

Unlike AVNRT or AVRT, this rhythm does not require a loop through the AV node to keep going.

Labeled cutaway heart showing an extra electrical focus in the right atrium, separate from the SA node, with signals spreading across the atria and through the AV node to the ventricles. — **An atrial signal before each beat:** This example shows distinct P waves before the narrow QRS spikes. The P waves come from the extra atrial source and can look different from those in normal sinus rhythm. Here, each atrial signal reaches the ventricles; other conduction patterns can occur. This is an illustrative example, not a patient recording; timing and voltage are not calibrated. P-wave appearance varies with the source location.

Why does the type matter?

Different SVTs require different treatment targets. An electrophysiologist, or EP, identifies the electrical pathway or source responsible for your rhythm and discusses the best treatment options.

Many common SVTs can be treated very effectively with catheter ablation, which targets the tissue sustaining the abnormal rhythm.

The key idea: SVT describes several fast electrical rhythms. Understanding which type you have helps explain why it happens—and how we can treat it.

Do I need a blood thinner for SVT?

AVNRT, AVRT, and focal atrial tachycardia do not routinely require blood thinners for stroke prevention. They do not carry the same established clot-related stroke risk as AFib or atrial flutter.

You may still need a blood thinner for another condition. Do not stop a prescribed blood thinner without discussing it with your care team.

Sources & further readingAHA: Fast heart rate and SVT ACC/AHA/HRS guideline: SVT management ACC CardioSmart: Living with SVT ACC CardioSmart: Questions to ask

Updated October 2026. Educational information; your own care plan may differ.

Supraventricular tachycardia (SVT)