No known history of prolonged QT syndrome Participant has long QT Syndrome at screening. Patients with a prior history of drug-induced serotonin syndrome, or a family history of long-QT syndrome Current or history of ventricular or life-threatening arrhythmias or diagnosis of long-QT syndrome History of risk factors for TdP, including family history of long QT syndrome. History or family history of long QT syndrome. History of long-QT syndrome Subjects with Long QT Syndrome at Screening. Clinically significant cardiac abnormalities including QRS duration of >120 msec; QTcF >470 msec for women and >450 msec for men; Abnormal cardiac rhythm; Clinically significant cardiac valve abnormality; Documented history of left ventricular ejection fraction <0.30 within 6 months; Permanent pacemaker or automatic implantable cardioverter defibrillator; History of torsades de pointes, congenital long QT syndrome, or family history of long QT syndrome or sudden death History of long QT syndrome or a family member with this condition Current or history of ventricular or life-threatening arrhythmias or diagnosis of long-QT syndrome Family history of long QT syndrome or other risk factors for torsades de pointes, and/or the use of concomitant medications that prolong the QT/QTc interval Long QT Syndrome Subject with a history of Long QT Syndrome at screening. At increased risk for developing prolonged QT interval, including hypokalemia or hypomagnesemia, unless corrected to within normal limits prior to first dose of SNX-5422; congenital long QT syndrome or a history of torsade de pointes; currently receiving anti-arrhythmics or other medications that may be associated with QT prolongation. History of risk factors for TdP, including family history of long QT syndrome Long QT syndrome or a known family history of long QT syndrome Patients who are taking medications that prolong QT interval and have a risk of Torsades de Pointes (Appendix F) or who have a history of long QT syndrome Subject is known to have long QT syndrome. Patients with a history of long-QT syndrome or documented family history of long-QT syndrome; patients who must remain on drugs that prolong the QT interval Patients with a known history or predisposition to cardiac conduction interval abnormalities, including QT Syndrome, or known family history of long QT Syndrome or taking medications that are known to prolong the QT interval. At increased risk for developing prolonged QT interval, including hypokalemia or hypomagnesemia, unless corrected to within normal limits prior to first dose of SNX-5422; congenital long QT syndrome or a history of torsade de pointes; currently receiving anti-arrhythmics or other medications that may be associated with QT prolongation Congenital long QT syndrome, prolonged QT interval, or family history of sudden unexplained death or long QT syndrome Diagnosis of or suspicion of long QT syndrome (including family history of long QT syndrome); History of long QT syndrome. Familial short QT syndrome Grade 3 or higher recent (within the past 6 months) or ongoing cardiac dysrhythmias, family history of long QT syndrome, or serum potassium < 3.0 mEq/L that is persistent and refractory to correction QTCF > 450 ms, inability to measure QT interval on ECG, personal or family history of long QT syndrome, requirement for medications that have the potential to prolong the QT interval Subject has a history (or family history) of long QT syndrome. A history of clinically significant electrocardiography (EKG) abnormalities, including QT prolongation, a family history of prolonged QT interval syndrome, or myocardial infarction (MI) within 6 months of study entry; patients with rate-controlled atrial fibrillation/flutter will be allowed on study History of, or at risk for, cardiac disease (e.g., long QT syndrome [> 450 msec] or concurrent treatment with any medication that prolongs QT interval). Subject with Long QT Syndrome. History of Brugada syndrome, risk factors for TdP, or family history of long QT syndrome.