Tachycardia refers to any heartbeat greater than 100 beats per minute. This can originate from the top of the heart and above the ventricle, and therefore is called a supraventricular tachycardia (SVT), or from the ventricle (bottom chamber). Patients may have no symptoms. This is more common with increasing age. For patients who do experience symptoms, these include palpitations, shortness of breath, dizziness and skipped beats. The patient often perceives the irregular heartbeat as very unpleasant. Loss of consciousness may result if the heart rate becomes too rapid. An implantable cardioverter-defibrillator (ICD) delivers electroshocks to terminate tachycardias.