Tachycardia is a heart rate of over 100 beats per minute. Heartbeats may have a regular or irregular rhythm.   Symptoms: - palpitations (a feeling in the chest that the heart is pounding or beating very fast) - chest pain - dizziness - swooning - fainting if the heart beats too fast for the blood to circulate well.   Ventricular Tachycardia When the fast heartbeat begins in the ventricles, what is called ventricular tachycardia, it may interfere with the heart's ability to pump enough blood to the brain and other vital organs. This type of arrhythmia can become ventricular fibrillation without any sort of warning.   Ventricular Fibrillation Ventricular fibrillation is one of the most serious heart rhythm alterations. In this rhythm, the ventricles tremble and the heart does not pump any blood. Death occurs quickly unless immediate medical reanimation is performed. If treated in time, ventricular tachycardia and ventricular fibrillation sometimes can become a normal rhythm with an electrical discharge. An effective way to treat these potentially fatal rhythms is through the use of an electronic device called implantable cardiac defibrillator. Fast heart rhythm can be controlled with medications or identifying and destroying the source of the rhythm alterations.   Supraventricular Tachycardia Supraventricular tachycardia is fast heartbeats that begin in the atria. In atrial fibrillation, the atria tremble instead of beating efficiently. The atria beat at over 300 beats per minute. This reduces the heart's efficiency because less blood flows through the atria toward the ventricles.   Sinusal Tachycardia Tachycardia also originates in the sinoatrial node. This is called sinusal tachycardia. It occurs when the heart's natural pacemaker sends signals to the heart for it to be faster than normal. This may occur naturally during exercise or when a person has stress. It may also occur when certain diseases exist and the demand on the heart is greater than normal.