Figure 3. Cell fusion demonstrated in two models of heterotopic cardiac xenotransplantations. The donor hamster (A) or mouse (B) heart is transplanted into the abdominal cavity of a GFP⁺ transgenic rat. The transplanted heart suffers tissue damage and remodeling and recruits circulating GFP⁺ cells, which engraft the heart and home preferentially into areas of tissue remodeling. GFP⁺ cells occasionally fuse with resident cardiomyocytes, thus generating hybrid cardiomyocytes expressing both GFP and donor markers, that is, hamster surface antigen (A) or nuclear lacZ (B).