There is a scarcity of source material available in animal models appropriate to test pediatric-size blood pump design for assisting the left ventricle. A juvenile ovine animal model was developed to evaluate two pediatric ventricular assist devices (VADs). The child-size Jarvik 2000 and CircuLite VADs were tested with this model. The 33 in vivo experiments were retrospectively studied to evaluate the reliability of the animal model. Dorset hybrid juvenile sheep (20~36 kg) were used to evaluate the small pediatric VADs. Under general anesthesia, a left lateral thoracotomy was performed through the fifth intercostal space. The devices were implanted between the left ventricle apex and the descending aorta without cardiopulmonary bypass. Heparin was infused continuously for anticoagulation therapy. Support duration averaged 26.7 ± 19.6 days. Completion of 75.7% (25/33) experiments was done as intended. The animals were docile and did not require sitters beyond the immediate operative period. Complication includes leg injury, graft infection, gastrointestinal bleeding, intravenous line disconnection, weight loss, renal failure, red urine, (one for each) and pulmonary failure in two. Activated clotting time was adjusted via continuous intravenous heparin to 150–200 seconds. Reliable hemodynamics and biocompatibility data were collected for evaluate pediatric intracorporeal VADs in the animal model. The juvenile sheep model is reliable, reproducible, and translatable for testing pediatric VADs. These experiments provided vital information for improvement of the devices and for clinical application in the future.