Abstract BACKGROUND: Tetrahydrocannabinol (THC), the psychoactive compound in cannabis, is increasingly used recreationally, especially among young adults. Although often perceived as harmless, emerging evidence links THC to serious cardiovascular complications, including QTc prolongation, ventricular arrhythmias, and sudden cardiac arrest, even in individuals without underlying heart disease. CASE REPORT: A 26-year-old woman with a history of chronic cannabis use was brought to the Emergency Department (ED) after having a sudden cardiac arrest. Her initial rhythm was ventricular fibrillation, and return of spontaneous circulation was achieved following advanced cardiac life support. An initial electrocardiogram revealed sinus tachycardia with a QTc interval of 483 ms, and a urine drug...