Abstract Body: Heart failure remains the leading cause of death in the U.S., and 50% of patients with heart failure still die within 5 years after diagnosis. Mitochondrial impairment and contractile dysfunction are the hallmarks of heart failure with reduced ejection fraction (HFrEF). Yet, there is currently no therapeutic strategy targeting both mitochondria and muscle contractility. PERM1 is a striated-muscle-specific regulator of mitochondrial bioenergetics and is predominantly expressed in the heart and skeletal muscle. Our recent studies demonstrated that PERM1 is downregulated in human and mouse HFrEF hearts and that loss of PERM1 in mice leads to reduced contractility and energy reserve in the heart. However, it is largely unknown whether PERM1 positively regulates both muscle contractility and energetics in the heart. Here, we performed the gene delivery of Perm1 to the heart in C57BL6 wild-type mice (8-12 weeks old) through retro-orbital injection of the adenovirus-associated virus (AAV)9 vector carrying Perm1 (AAV-PERM1). The protein expression levels of PERM1 in the heart was increased by 3 fold as compared with control (mice injected with AAV9-GFP vectors), while there was no change in PERM1 expression in skeletal muscle (n=4/group). Strikingly, AAV-PERM1 mice exhibited a significant increase in ejection fraction (EF) and fractional shortening (FS) (AAV-GFP vs. AAV-PERM1: 0.93 vs. 1.43 and 0.92 vs. 1.64 in DEF and DFS, respectively, both p<0.05 in t-test). In addition, we observed a subtle, yet significant increase in the ratio of the heart weight to tibial length in AAV-PERM1 mice (AAV-GFP vs. AAV-PERM1: 4.7 vs 5.97, p<0.05 in t-test), suggestive of moderate cardiac hypertrophy development. Furthermore, PERM1 overexpression in the heart increased the mitochondrial copy number by 38% as compared to control AAV-GFP mice (p<0.05 in t-test), concurrently with an upregulation of the mitochondrial bioenergetics master regulator PGC-1α (155% of control, p<0.05 in t-test). Overall, these results showed that AAV-mediated PERM1 overexpression simultaneously enhances muscle contractility and mitochondrial biogenesis in the heart. This study further suggests that the gene delivery of PERM1 could be a potential therapeutic approach to treat HFrEF patients.