There are several recent reports of tetrahydrocannabinol vaping-related sudden cardiac arrest, and the mechanisms are unclear. We report a unique case of a 19-year-old female who suffered documented prolonged QTc leading to Torsades de pointes and cardiac arrest in the setting of frequent marijuana wax vaping. While she demonstrated normal baseline QTc measurements years earlier, she was found to have a genetic predisposition to QTc prolongation (genetic mutation, family history of prolonged QTc), suggesting that specific patient populations are at higher risk of these adverse events. The patient was acutely managed with isoproterenol to increase the heart rate and was discharged on nadolol after placement of an implantable cardioverter-defibrillator. Marijuana wax vaping and dabbing may cause fatal Torsades de pointes in susceptible patients, and further research is required to identify these patients a priori.