Abstract Objectives. We sought to quantitate the incidence of malignant ventricular arrhythmias and to identify subsequent hemodynamic changes and untoward events in patients who have received an implantable left ventricular circulatory assist device as an extended bridge to heart transplantation. Background. Implantable long-term mechanical circulatory assist devices have been used clinically with increasing frequency and success for the past 4 years. Previous investigators have suggested that patients with malignant ventricular arrhythmias receiving a left ventricular assist device will require both left and right ventricular assistance to maintain vital organ perfusion. Methods. We reviewed our 4-year experience with 21 patients who underwent implantation of a left ventricular assist device. Device flows and mean arterial pressure were used to assess systemic perfusion; central venous pressure provided a gauge of right ventricular function. Charts were screened for evidence of end-organ injury resulting from malignant ventricular arrhythmias. Results. Malignant ventricular arrhythmias occurred in 4 patients (19%) before device placement and in 9 patients (43%) during device support. The latter nine patients formed the final study group; their arrhythmias occurred 0 to 186 days after device implantation and had a duration of 10 min to 12 days. The patients reported weakness or palpitation; however, none reported syncope or dyspnea. Mean arterial pressure and central venous pressure were insiganificantly changed by the arrhythmias. Device flow decreased by 1.4 ± 0.6 liters/min (p < 0.05) at the onset of the arrhythmias but returned to normal after cardioversion. No thromboembolic events or significant end-organ dysfunction occurred. Conclusion. Absence of right ventricular contraction during malignant ventricular arrhythmias is well tolerated in recipients of a left ventricular assist device. The diagnosis of malignant arrhythmia should be suspected if an unexplained decrease in left ventricular assist device flow occurs. Early electrical cardioversion is warranted to avoid both thrombus formation in the native heart and right ventricular myocardial injury from prolonged fibrillation.