Objectives: We investigated whether trimetazidine pretreatment can regulate central and peripheral serotonin (5-HT) in rats of myocardial infarction (MI) combined with depression. Methods: Forty rats were randomly assigned to a sham operation group (n = 10) and a disease model group (n = 30).The sham operation group was pretreated with normal saline for 4 weeks. The disease model group was randomly assigned further into a negative control subgroup, a positive control subgroup, and a treatment subgroup - the groups received saline, sertraline, and trimetazidine pretreatment, respectively, for 4 weeks, then the rats were subjected to MI combined with depression. 5-HT concentrations in the serum, platelet lysate, and cerebral cortex lysate were analyzed with ELISA. Results: The levels of serum 5-FIT and platelet 5-HT were significantly lower in negative control subgroup than the sham operation group (P < 0.05), but there was no significant difference in brain 5-HT (P > 0.05). Compared with the negative control subgroup, the levels of serum 5-HT and platelet 5-FIT in the positive control subgroup and treatment subgroup were significantly higher (P < 0.05). The levels of 5-FIT in brain of the positive control subgroup and treatment subgroup were significantly lower than those in the negative control subgroup (P < 0.05). Conclusions: Trimetazidine pretreatment can increase serum and platelet 5-HT levels in rats with MI and depression and decrease 5-HT levels in brain tissue. This regulatory effect on central and peripheral 5-HT suggests a role for trimetazidine in the treatment of psychocardiological diseases.