The clinical presentation of SVT is age and duration dependent. In infants with paroxysmal SVT, the heart rate is usually 220 to 320 beats/minute; in older children, it is 160 to 280 beats/minute.6 In infants, symptoms are usually nonspecific and include poor feeding, irritability, vomiting, cyanosis, and pallid spells. If the symptoms are unrecognized for hours to days, the infant can present with significant hemodynamic compromise or heart failure symptoms.12 It is rare for infants who have SVT for less than 24 hours to develop signs of congestive heart failure at the time of presentation; however, congestive heart failure is present in 19% of infants who have SVT for 24 to 36 hours and in 50% who have SVT for more than 48 hours.6 Approximately 20% of infants receive a diagnosis during routine office visits and during asymptomatic episodes.6,8 In verbal children with SVT, palpitations and fluttering in the chest are the usual presenting symptoms. Because reentrant arrhythmias are a circuit, they tend to be all or nothing, and the onset is frequently described as being abrupt, similar to a light switch being turned on. The offset may be less dramatic because the catecholamine level is typically elevated, with resultant sinus tachycardia at the termination of SVT and subsequent gradual slowing. Frequently, lightheadedness and dizziness due to transient hypotension can occur at the onset, but syncope is rare in SVT, and its presence should raise suspicion of something other than SVT. The frequency and duration of the episodes vary greatly from a few minutes to a few hours and occur as often as daily or as infrequently as once or twice per year. Although they are rare in verbal children, incessant SVT symptoms may go unrecognized until cardiac dysfunction develops.