A serious cardiac arrhythmia in which each heartbeat is initiated from electrical activity in the ventricles rather than from the sinoatrial node in the right atrium, It is caused by an abnomally fast heartrate due to serious heart disease, such as myocardial infarction or cardiomyopathy.

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Tachycardia

Tachycardia is a faster than normal heart rate. A healthy adult heart normally beats 60 to 100 times a minute when a person is at rest. If you have tachycardia (tak-ih-KAHR-de-uh), the rate in the upper chambers or lower chambers of the heart, or both, are increased significantly.                          In some cases, tachycardias may cause no symptoms or complications. However, tachycardias can seriously disrupt normal heart function, increase the risk of stroke, or cause sudden cardiac arrest or death.

Symptoms

By Mayo Clinic Staff

When your heart's rate is too rapid, it may not effectively pump blood to the rest of your body, depriving your organs and tissues of oxygen. This can cause these tachycardia symptoms:

Dizziness
Shortness of breath
Lightheadedness
Rapid pulse rate
Heart palpitations — a racing, uncomfortable or irregular heartbeat or a sensation of "flopping" in the chest
Chest pain
Fainting (syncope)

Some people with tachycardia have no symptoms, and the condition is only discovered during a physical examination or with a heart-monitoring test called an electrocardiogram.

When to see a doctor
A number of conditions can cause a rapid heart rate and tachycardia symptoms. It's important to get a prompt, accurate diagnosis and appropriate care. See your doctor if you or your child experiences any tachycardia symptoms.

If you faint, have difficulty breathing or have chest pain lasting more than a few minutes, get emergency care, or call 911 or your local emergency number. Seek emergency care for anyone experiencing these symptoms.