To examine whether nitric oxide (NO) has a protective effect against Ca 2+ overdose or a beneficial action on myocardial cells, we employed direct gene-transfer of endothelial (type 111) nitric oxide synthase (eNOS), using HVJ (Sendai virus) coated liposomes and beta-galactosidase (lac-z) as a marker for the transfection. The transfection efficiency of the lac-z gene was comparable with adenovirus as a vector, though the subsequent inflammation was much improved. The lac-z gene transfection was restricted to myoplasm between two intercalated discs, indicating that the transfected gene does not permeate the disc. Co-transfection with human eNOS gene revealed degraded myoplasm of not only transfected cells but adjacent myocytes, fibrotic changes and infiltration of mononuclear cells seven days after the transfection. Electron microscopy of the lesions revealed a huge accumulation of mitochondria and loss of myofilaments, though fragmentation of nucleus or cytoplasm was not obvious. We conclude that an expression of human eNOS gene in cardiomyocytes causes a degenerative process, incompatible with typical apoptosis.