Tachycardia =Too fast
A heart rate of more than 100 beats per minute (BPM) in adults is called tachycardia. What’s too fast for you may depend on your age and physical condition.

Types of tachycardias

• Atrial or Supraventricular tachycardias  start either in the upper chambers (atria) or the middle region (AV node or the very beginning portion of the His-Purkinje system.
  Watch an animation of atrial tachycardia

• Sinus tachycardia  is a heart rate that’s faster than normal but the heart functions properly.

• Ventricular tachycardias start in the lower chambers - the ventricles. Can be life-threatening.  Watch an animation of ventricular tachycardia.

Causes of tachycardia

• Under certain conditions, the automatic firing rate of secondary pacemaker tissue may become too fast. If such an abnormal "focus" fires faster than the sinus node, it may take over control of the heart rhythm and cause tachycardia.

• In another type of abnormal conduction, impulses get caught in a merry-go-round-like sequence. This process, called reentry, is a common cause of tachycardia.

Symptoms of tachycardia
Rapid heart beating can produce detectable symptoms including:

• Palpitations
• Heart pounding or racing
• Dizziness
• Lightheadedness
• Fainting or near fainting
• Rhythm may be fast and regular or fast and irregular.

Treatments for tachycardia

• Sudden ventricular tachycardia and ventricular fibrillation are life-threatening. With rapid detection they can be converted into a normal rhythm with electrical shock from a defibrillator.

• Rapid heart beating can be controlled over time with medications and by identifying or destroying the focus of rhythm disturbances.

• One effective way of correcting these life-threatening rhythms is by using an electronic device called an implantable cardioverter defibrillator (ICD).