Tachycardia is the name of the heart arrhythmia condition that is characterized by an overly rapid heartbeat. Different types of tachycardia include junctional tachycardia, paroxysmal atrial tachycardia (PAT), ventricular tachycardia and supraventricular tachycardia. These conditions occur due to a problem with the heart’s electrical impulses that causes them to fire at irregular intervals. In children, the most common heart rhythm disorder is supraventricular tachycardia, or SVT. Kids with SVT may experience a pounding feeling in their chest along with dizziness and the feeling that they are going to pass out. This and other types of tachycardia do not always require advanced medical treatment, but should be closely evaluated and monitored by your physician.