People of all ages, including infants, can experience the symptoms related to WPW.

Symptoms of WPW syndrome are the result of a fast heart rate. They most often appear for the first time in people in their teens or 20s. Common symptoms of WPW syndrome include:

• Sensation of rapid, fluttering or pounding heartbeats (palpitations)
• Dizziness or lightheadedness
• Shortness of breath
• Fainting
• Fatigue
• Anxiety

An episode of a very fast heartbeat can begin suddenly and last for a few seconds or several hours. Episodes can occur during exercise or while at rest. Caffeine or other stimulants and alcohol may be a trigger for some people.

Over time, symptoms of WPW may disappear in as many as 25 percent of people who experience them.

Symptoms in more-serious cases

About 10 to 30 percent of people with WPW syndrome occasionally experience a type of irregular heartbeat known as atrial fibrillation. In these people WPW signs and symptoms may include:

• Chest pain
• Chest tightness
• Difficulty breathing
• Fainting

Symptoms in infants

Signs and symptoms in infants with WPW syndrome may include:

• Ashen color
• Restlessness or irritability
• Rapid breathing
• Poor eating

Causes

The extra electrical pathway in your heart that causes a rapid heartbeat is present at birth. An abnormal gene is the cause in a small percentage of people with WPW. The syndrome also is associated with some forms of congenital heart disease, such as Ebstein's anomaly.

Otherwise, little is known about why the extra pathway develops. WPW is more common in males than in females.

Normal heart electrical system

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by a mass of tissue in the right atrium (sinus node). The sinus node produces electrical impulses that generate each heartbeat.

These electrical impulses travel across the atria, causing muscle contractions that pump blood into the ventricles. The electrical impulses then arrive at a cluster of cells called the atrioventricular (AV) node — usually the only pathway for signals to travel from the atria to the ventricles. The AV node slows the electrical signal before sending it to the ventricles.

This slight delay allows the ventricles to fill with blood. When electrical impulses reach the ventricles, muscle contractions pump blood to the lungs and the rest of the body.

Abnormal electrical system in WPW

In WPW syndrome, an extra electrical pathway connects the atria and ventricles, allowing electrical impulses to bypass the AV node. When the electrical impulses use this detour through the heart, the ventricles are activated too early.

The extra electrical pathway can cause two major types of rhythm disturbances:

• Looped electrical impulses. In WPW, the heart's electrical impulses travel down either the normal or the extra pathway and up the other one, creating a complete electrical loop of signals. This condition (AV reentrant tachycardia) sends impulses to the ventricles at a very rapid rate. As a result, the ventricles pump very quickly, causing rapid heartbeat.
• Disorganized electrical impulses. If electrical impulses don't begin correctly in the right atrium, they may travel across the atria in a disorganized way, causing atrial fibrillation. The disorganized signals and the extra pathway of WPW also can cause the ventricles to beat faster. As a result, the ventricles don't have time to fill with blood and don't pump enough blood to the body.

For many people, WPW syndrome doesn't cause significant problems. But complications can occur, and it's not always possible to know your risk of serious heart-related events. If the disorder is untreated, and particularly if you have other heart conditions, you may experience:

• Fainting spells
• Fast heartbeats
• Rarely, sudden death