This case report presents a detailed analysis of a 28-year-old woman who experienced sudden cardiac arrest (SCA). The patient had a history of marijuana consumption and was also diagnosed with a congenital ventricular septal defect (VSD) with no prior intervention or treatment. VSD is a common acyanotic congenital heart disease, which poses a constant risk of premature ventricular contractions (PVCs). During the evaluation, the patient's electrocardiogram PVCs and a prolonged QT interval were revealed. This study highlights the risk associated with the administration or consumption of drugs that can prolong the QT interval in patients with VSD. It also indicates that patients with VSD and who have a history of marijuana consumption should be cautioned about the risk of arrhythmias causing SCA due to prolonged QT interval caused by the cannabinoid. This case emphasizes the requirement of cardiac health monitoring in individuals with VSD and caution while prescribing medications that can affect the QT interval leading to life-threatening arrhythmias.