For patients with end-stage heart failure (HF), the use of mechanical circulatory support (MCS) is an increasingly used strategy for the management of patients with advanced HF as a bridge to transplantation, destination therapy, or acute circulatory support. Although these devices effectively improve survival, ventricular arrhythmias (VAs) and atrial arrhythmias (AAs) are common in MCS device recipients. The management of arrhythmias can be a challenge when they become refractory to medication or to device therapy, and their impact on prognosis can be detrimental despite the mechanical support. An increasing number of studies have attempted to address issues regarding arrhythmia management in patients with MCS. Multiple comorbidities often affect patients, requiring multidisciplinary interventions to achieve clinical stability. Correction of irreversible factors, knowledge of underlying heart disease, careful optimization of devices, antiarrhythmic drugs, and catheter ablation (CA) play a crucial role. This chapter will summarize the epidemiology, underlying mechanisms, and management strategies for the arrhythmias, especially focusing on intractable, life-threatening arrhythmias in patients with MCS devices.