BACKGROUND As early perioperative survival with left ventricular assist device support improves, additional emphasis must be placed on patient rehabilitation. Especially as mean left ventricular assist device support times exceed 100 days, it is essential for health professionals to mobilize patients to prevent the incidence of the deleterious effects of bedrest. The timing of optimal functional performance and the safety of rehabilitation has not been described. METHODS We retrospectively studied patients surviving left ventricular assist device implantation (34 of 41 patients; 27 men, 7 women; age 51 +/- 11 years). Physical therapy consisted of progressive mobilization leading to treadmill exercise or cycling. All patients exercised in the "pump on full" mode with flows >or= 3.0 L/min. RESULTS Twenty of thirty-four patients initiated ambulation at 7 to 10 days with independent ambulation by 14 days in 55% of the group. Treadmill exercise was tolerated by 82% of the patients, begun at postoperative day 21 by eighteen patients. The greatest improvement in exercise performance was seen by 6 to 8 weeks (20 to 30 minutes at 3.17 +/- 0.79 metabolic equivalents). Maximal functional capacity achieved was influenced by medical complications. A total of 1878 treatment sessions lasting 1390 hours was performed. Only four minor incidents occurred representing 2.9 incidents/1000 patient hours; all involved a transient decrease in pump flow. None of these events resulted in an increase in morbidity or mortality. CONCLUSIONS Progressive mobilization in patients with left ventricular assist device is safe. Patients return to independence in activities of daily living and tolerate prolonged workloads of up to 5 metabolic equivalents. There is rapid improvement in functional capacity until 6 weeks after operation. Delay in transplantation until this time may optimize postoperative recovery.