[Objective]This study was designed to investigate the effects of 5-aminoimidasole-4-carboxamide ribonucleoside (AICAR)on activity of transcription factor Forkhead O 3a(FOXO3a)and expression of ubiquitin ligase muscle atrophy F-box (MAFbx),and to explore the role of adenosine monophosphate-activated protein kinase(AMPK)on proteolysis pathways in eardiomyocytes.[Methods]The effect of AICAR on activation of AMPK was observed.Cultured neonatal rat cardiomyocytes was treated with AICAR in different concentration.Cultured cardiomyocytes were then divided into three groups:control group,AICAR group,AICAR+Compound C group.Effects of AMPK activation on phosphorylation of FOXO3a and expression of MAFbx in cardiomyocytes were detected using Western blot.[Results]①Compared with control group,activity of AMPK in cultured cardiomyocytes was increased after treatment with 0.25 mmol/L or 0.5 mmol/L AICAR for 6 h(P＜0.05),and the activity of AMPK was further enhanced after treatment with 1.0 mmol/L or 2.0 mmol/L AICAR for 6 h(P＜0.01).②Activation of AMPK by AICAR significantly increased the transcriptional activity of FOXO3a(P＜0.01),and enhanced MAFbx protein expression in cardiomyocytes when comparing with control group(P＜0.01),however,specific AMPK antagonist Compound C markedly reversed these effects induced by AICAR.[Conclusion]AMPK may regulate cardiomyocytes proteolysis by activation of FOXO3a transcription factor,and up-regulation of MAFbx protein expression.