Inclusion Criteria:  A patient will be eligible for study participation if they meet all of the following criteria:  Has completed a Milestone Pharmaceuticals Inc. clinical research trial of etripamil NS for the treatment of PSVT (NODE-301, NODE-302, or NODE-303), and experienced no significant safety issues during participation as per the Investigator's opinion. Has signed the MSP-2017-1278 written informed consent;  Women of childbearing potential who are sexually active with a male partner who is not surgically sterile (i.e., vasectomy) must be willing to use at least 1 form of highly effective contraception from the time of signed informed consent until 7 days after the last administration of etripamil NS and must be willing to discontinue from the study should they become or plan to become pregnant.  The following categories define females who are not considered to be of childbearing potential:  Postmenopausal females, defined as having amenorrhea for at least 12 months without an alternative medical cause; or  Premenopausal females with 1 of the following:  Documented hysterectomy; or Documented bilateral salpingectomy; or Documented bilateral oophorectomy; or  All females who do not meet at least one of the above criteria are considered to be of childbearing potential  Willing and able to comply with Investigator instructions on etripamil NS use and study requirements.  Exclusion Criteria:  A patient will be excluded from the study if they meet any of the following criteria:  History of allergic reaction to verapamil, etripamil, or any of the investigational medical components; Current chronic therapy with digoxin, or any Class I or III antiarrhythmic drug. Patients may be eligible if these drugs are stopped at least five half-lives before enrollment. The only exception is oral amiodarone which must be stopped 30 days before enrollment; History of ventricular pre-excitation, e.g., delta waves, Wolff-Parkinson-White syndrome; History of a second- or third-degree atrioventricular block; History of sick sinus syndrome and marked bradycardia (≤40 beats/minute); History or evidence of severe ventricular arrhythmia (e.g. torsades de points, ventricular fibrillation, or sustained ventricular tachycardia) Symptoms of congestive heart failure New York Heart Association Class II to IV; Significant physical or psychiatric condition including alcoholism or drug abuse, which, in the opinion of the Investigator, could jeopardize the safety of the patient, or impede the patient's capacity to follow the study requirements; Syncope due to an arrhythmic etiology or unexplained syncope during or after participation in an etripamil clinical research trial; Is pregnant, breastfeeding, or is planning to become pregnant during the study; History of acute coronary syndrome or stroke within 6 months of enrollment; Evidence of symptoms of hypotension within 24 hours following previous administration of etripamil.