Multiple molecular mechanisms are involved in the development of heart failure (HF) after myocardial infarction (MI). However, interventions targeting these pathological processes alone remain clinically ineffective. Therefore, it is essential to identify new therapeutic targets for alleviating cardiac dysfunction after MI. Here, gain- and loss-of-function approaches were used to investigate the role of reticulon 3 (RTN3) in HF after MI. We found that RTN3 was elevated in the myocardium of patients with HF and mice with MI. Cardiomyocyte-specific RTN3 overexpression decreased systolic function in mice under physiological conditions and exacerbated the development of HF induced by MI. Conversely,