Several of the current techniques for transfer of both oligonucleotide and plasmid DNA into the myocardium are impaired by low efficiency and toxicity. To improve gene transfer techniques, especially into the whole heart, a gene transfer method involving liposome in conjunction with a viral envelope (HVJ-liposome) was essayed as an alternative. FITC-labeled oligonucleotide (F-ODN) and the cDNA of beta-galactosidase (beta-gal) were introduced into the myocardium by coronary infusion of HVJ-liposome during cardioplegic arrest of adult Sprague-Dawley rat hearts. Then, transfected heart was ectopically transplanted into another rat abdomen of the same strain to maintain the transfected heart long enough to allow for protein synthesis. After 3 days of transfection, transfected heart was excised and the efficiency of gene transfection was evaluated. FITC was detected in the nuclei of more than 70% of the myocytes and endothelial cells both in the epicardium and endocardium. beta-Gal was expressed in the cytosol of more than 50% of the myocytes. beta-Gal expression was demonstrated by Western blotting analysis at day 3 after transfection and continued for at least 14 days. No significant histological damage of the myocardium or leakage of CPK were detected in the rats transfected by the HVJ-liposome method. These results clearly demonstrate that the hearts were efficiently transfected both by oligonucleotide and plasmid DNA as a result of coronary infusion of HVJ-liposome during cardioplegic arrest. This thus appears to be an efficient method for gene transfer into the whole heart, providing a new tool for research and therapy for heart diseases.