OBJECTIVE: Cardiovascular mortality in schizophrenia and bipolar disorder patients is more than double that of the general population. There appears to be a dual effect between cardiovascular diseases and schizophrenia and bipolar disorder. Inflammation and increased oxidative stress cause cardiac remodeling and increase the severity of psychiatric illness. METHODS: Echocardiographic imaging was performed simultaneously with serum samples obtained for asymmetric dimethylarginine, symmetric dimethylarginine, monomethyl-L-arginine, arginine and its metabolites, and galectin 3 levels in 80 patients with bipolar disorder who were euthymic for at least 8 weeks and 69 patients with schizophrenia undergoing treatment. RESULTS: Monomethyl-L-arginine and arginine levels were significantly higher in bipolar disorder patients compared to schizophrenia patients. Galectin 3 level was significantly higher in bipolar disorder patients with psychotic symptoms compared to schizophrenia patients. There was no significant difference between the groups in terms of other parameters. Statistically significant differences were found between bipolar disorder and schizophrenia patients in terms of diastolic diameter (mm), systolic diameter (mm), interventricular septum (mm), left atrium (mm), and posterior wall (mm) values. CONCLUSION: Arginine and its metabolites, asymmetric dimethylarginine, symmetric dimethylarginine, and galectin 3, may be important biomarkers of cardiovascular diseases risk. In this study, changes in biochemical parameters and cardiac structure could not be explained by disease severity.