Both microRNAs (miRs) and dexmedetomidine (Dex) have been verified to exert functional roles in myocardial ischemia-reperfusion injury (MI/RI). Given that, we concretely aim to discuss the effects of Dex and miR-138-5p on ventricular remodeling in mice affected by MI/RI via mediating leukotriene B4 receptor 1 (Ltb4r1). MI/RI mouse model was established by ligating left anterior descending coronary artery. The cardiac function, inflammatory factors and collagen fiber contents were detected after Dex/miR-138-5p/Ltb4r1 treatment. MiR-138-5p and Ltb4r1 expression in myocardial tissues were tested by RT-qPCR and western blot assay. The target relationship between miR-138-5p and Ltb4r1 was verified by online software prediction and luciferase activity assay. MiR-138-5p was down-regulated while Ltb4r1 was up-regulated in myocardial tissues of MI/RI mice. Dex improved cardiac function, alleviated myocardial damage, reduced inflammatory factor contents, collagen fibers, and Ltb4r1 expression while increased miR-138-5p expression in myocardial tissues of mice with MI/RI. Restored miR-138-5p and depleted Ltb4r1 improved cardiac function, abated inflammatory factor contents, myocardial damage, and content of collagen fibers in MI/RI mice. MiR-138-5p directly targeted Ltb4r1. The work evidence that Dex could ameliorate ventricular remodeling of MI/RI mice by up-regulating miR-138-3p and down-regulating Ltb4r1. Thus, Dex and miR-138-3p/Ltb4r1 may serve as potential targets for the ventricular remodeling of MI/RI.