A, tissue levels of cGMP in Lenti.EF1α-nNOS-transduced atria after 4 months were significantly higher than those measured in the Lenti.EF1α-eGFP-treated group (*P < 0.05, unpaired t test, n= 8 in each group). B, tissue cAMP levels were also significantly increased after Lenti.EF1α-nNOS transduction compared to eGFP group (*P < 0.05, unpaired t test) (n= 8 in each group).