Since one of the attractions of gene therapy in the heart is the implantation of genetically modified cultured cells, we employed genetically modified myocytes transfected with FITC-labeled oligodeoxynucleotides (ODN) and beta-galactosidase gene in this study, to investigate the cellular localization and fate of grafted myocytes in the heart. In addition, we examined the feasibility of myocytes grafting into a myocardial infarction model. Delivery of FITC-labeled ODN with the HVJ-liposome method resulted in sustained fluorescence as compared to direct transfer of 'naked' ODN. Interestingly, implantation of cardiac myocytes transfected with FITC-labeled ODN ex vivo by the HVJ-liposome method resulted in sustained fluorescence for at least 1 week in the noninfarcted area, whereas little fluorescence was detected in the area of infarction. This observation was confirmed by measurement of fluorescence, which showed significantly higher levels in the noninfarcted area than the infarcted area. Positive staining for beta-galactosidase protein was also clearly observed 7 days after grafting of transfection of the beta-galactosidase gene, while no staining was detected in grafted myocytes in control rats. Survival of implanted genetically modified cardiac myocytes in the noninfarcted, but not infarcted area, provides new information for the local delivery of recombinant molecules to the heart using gene therapy.