The primary objective of this registry is to capture real-world safety and performance data on AtriCure devices used to ablate cardiac tissue when treating Inappropriate Sinus Tachycardia (IST) or Postural Tachycardia Syndrome (POTS). This is a retrospective and prospective, multicenter, US/OUS, observational data registry.

Inclusion Criteria:

1. Subject is scheduled to undergo or has undergone a procedure to treat IST or POTS using one or more AtriCure devices.
2. Subject is willing to provide written informed consent (defined as legally effective, documented confirmation of a subject's voluntary agreement to participate in this Registry) or authorization per institution and geographical requirements

Exclusion Criteria:

1. Subject is enrolled in a concurrent study that may impact treatment outcome of IST or POTS.
2. Subject with exclusion criteria required by FDA or local governance

The IST registry eligibility is open to sites and physicians performing the described treatments for patients diagnosed with IST and POTS. Subjects must have been scheduled to undergo or have undergone the described treatments for IST or POTS by their physicians. Registry participating sites will enroll patients that meet all inclusion criteria and no exclusion criteria without preselection or bias.