Subjects must have met both of the following acute and chronic conditions to be considered a chronic effectiveness (treatment) success: * Acute Success: The inability to induce more than one echo beat by the same pacing maneuvers that induced AVNRT before cryoablation (with drug provocation if required for induction before cryoablation) at the conclusion of the study cryoablation procedure assessment. * Chronic Success: Lack of documented recurrence of clinical AVNRT during the 6-month follow-up period after the study cryoablation procedure.

Subjects who had at least one safety event during or after their cryoablation procedure or through 6 months of follow-up are considered a primary (chronic) safety failure. A safety event is defined as the occurrence of any adverse event that is adjudicated by the AE Adjudication Committee as being serious and study ablation procedure-related and/or Freezor Xtra Catheter related that: 1) Resulted in death, 2) Resulted in a life-threatening illness or injury, 3) Resulted in permanent impairment of a body function or permanent damage to a body structure, 4) Necessitated significant intervention, such as major surgery or even intravenous medical therapy (e.g., vasopressors), to prevent permanent impairment of a body function or permanent damage to a body structure, or 5) Required in-patient hospitalization or a prolongation of an existing hospital stay.