BACKGROUND: Evidence on subclinical cardiac organ damage and, particularly on myocardial deformation, detected by speckle tracking echocardiography (STE), in patients with schizophrenia and bipolar disorder free from known cardiac disease is scanty. The aim of the present systematic review was investigate whether global longitudinal strain (GLS) could be a more sensitive index of systolic dysfunction than left ventricular ejection fraction (LVEF) in this setting, after having preliminary focused on LV structural and functional changes by standard echocardiography or magnetic resonance imaging (MRI). METHODS: To identify eligible studies targeting GLS in patients with schizophrenia and bipolar disorder systematic searches were conducted across bibliographic databases (Pub-Med, OVID, EMBASE and Cochrane library) following the PRISMA guidelines, from inception up to August 31, 2024. RESULTS: Six studies focusing on GLS including a total of 535 patients with schizophrenia (n = 185) or bipolar disorder (n = 350), and 153 healthy controls were considered for the review. Four studies compared GLS values of patients with schizophrenia and bipolar disorder with healthy controls and the other two studies evaluated the impact of antipsychotic therapy on this index of myocardial deformation. Overall, GLS emerged as a more sensitive index in assessing early systolic dysfunction than LVEF as well as the effects of antipsychotic drugs on systolic function. CONCLUSIONS: The evaluation of LV mechanics in patients with schizophrenia and bipolar disorder is underused despite the fact that could unmask subclinical systolic dysfunction better than LVEF. Thus, the role of STE in detecting early LV systolic dysfunction in this clinical setting needs to be further investigated in future studies.