BACKGROUND: The clinical application of targeted anti-programmed cell death protein 1 (PD-1) therapy has significantly improved the prognosis of patients with various advanced malignancies. However, life-threatening immune-related adverse events remain problematic, including rare but highly lethal myocarditis. Bidirectional ventricular tachycardia (BVT) is a rare but dangerous form of ventricular arrhythmia. If immune checkpoint inhibitor (ICI)-associated myocarditis is complicated with BVT, patients face an extremely high risk of mortality. CASE DESCRIPTION: The first case was a 45-year-old male with advanced intrahepatic cholangiocarcinoma who experienced sudden chest tightness after receiving 11 cycles of camrelizumab. Test results showed significantly elevated myocardial injury markers, and electrocardiography (ECG) indicated BVT; cardiac magnetic resonance imaging findings were consistent with acute myocarditis. A diagnosis of PD-1 inhibitor-associated myocarditis complicated with BVT was considered. Following immunotherapy discontinuation, the patient was treated with steroid therapy, antiarrhythmic drugs, and electrical cardioversion. This led to marked improvements in ICI-associated myocarditis, BVT resolution, and favorable outcomes. The second case was a 34-year-old female patient with type B1 thymoma who experienced sudden chest tightness, shortness of breath, and fatigue after receiving one second-line cycle of sintilimab. Significantly elevated myocardial injury markers were observed, and ECG findings indicated BVT. The patient was diagnosed with PD-1 inhibitor-associated myocarditis complicated with BVT. However, the patient was in critical condition. Despite receiving supportive therapies, including steroid therapy, antiarrhythmic drugs, electrical cardioversion, invasive mechanical ventilation, and extracorporeal membrane oxygenation, the patient's condition deteriorated rapidly, ultimately leading to death. CONCLUSIONS: These two cases demonstrate that although the incidence of malignant arrhythmias such as BVT in ICI-associated myocarditis is low, the risk of sudden death remains extremely high. Therefore, we consider dynamic monitoring of myocardial injury markers and ECG in patients with ICI-associated myocarditis. Additionally, our observations suggest that steroid therapy is a crucial treatment method for patients with ICI-associated myocarditis complicated with BVT. This report adds to the growing body of evidence indicating that BVT is an important yet previously infrequently described ECG manifestation of severe cardiotoxicity associated with ICIs.