Cardiac tissue engineering offers the prospect of a novel treatment for acquired or congenital heart defects. Previously, our studies have shown a significant mass of vascularized cardiac tissue can be generated using a vascularized tissue engineering chamber approach in nude rats. In this present study, syngeneic rats were investigated as an animal model for cardiac tissue engineering using the arteriovenous loop (AVL) chamber in the presence of a functional immune system. Neonatal cardiomyocytes implanted into the AVL chamber survived and assembled into a contractile flap confirming the basic features we previously showed in growing a cardiac construct. There was no significant loss of the assembled cardiac muscle from immune response. The engineered cardiac muscle flaps (ECMFs) formed were transplanted to the neck vessels of the same animal using a microsurgical technique, and all transplanted tissues remained contractile. The cardiac muscle volume of the control and transplant groups was estimated with histomorphometry using desmin and α-sarcomeric actin immunostaining, and there were no significant differences between the two groups. Finally, utilizing a novel model of transplantation, the ECMFs were transplanted to the heart of a recipient syngeneic rat as a vascularized tissue. The cardiac muscle within the transplanted ECMF was shown to survive and remain contractile for the 4-week post-transplantation period, and importantly, the cardiomyocytes retained the elongated, striated appearance of a mature phenotype. This study demonstrated the proof of concept for transplanting tissue-engineered cardiac muscle as a vascularized cardiac construct.