To investigate the effect of intracoronary injection of autologous mononuclear bone marrow stem cells (BMSCs) in patients with ST-elevation myocardial infarction (STEMI) on left ventricular (LV) systolic and diastolic function using standard echocardiography and 2-dimensional systolic strain. A total of 60 patients with first anterior wall STEMI and LV ejection fraction of <40%, treated with successful primary percutaneous coronary intervention were randomly assigned to the treatment group (BMSC group) or the control group in a 2:1 ratio. Transcatheter intracoronary injection of BMSCs into the infarct-related artery was performed 7 days after STEMI. Standard echocardiography and speckle tracking analysis was performed at baseline and 6 months after STEMI. No differences were found in the baseline echocardiographic parameters of LV systolic and diastolic dysfunction--the LV ejection fraction was 35 +/- 6% in the BMSC group, similar to that in the control group (33 +/- 7%, p = 0.42). After 6 months, the absolute change in the LV ejection fraction was significantly greater in the BMSC group than in the control group (10 +/- 9% versus 5 +/- 8%, p = 0.04). Significant improvement was seen in 2-dimensional systolic strain in all segments (12 +/- 4 vs 14 +/- 4; p = 0.0009) and in the infarcted area (5 +/- 2 vs 6 +/- 2; p = 0.0038) only in the BMSC group. Of the diastolic function parameters, we observed improvement in the early filling propagation velocity (30 +/- 8 cm/s vs 37 +/- 13 cm/s; p = 0.0008), early diastolic velocity - E' (4.5 +/- 1.5 vs 5.0 +/- 1.3, p = 0.02), and the E/E' ratio (17 +/- 7 vs 14 +/- 5; p = 0.03) in the BMSC group. In conclusion, intracoronary injection of unselected BMSCs in patients with STEMI improved both LV systolic and diastolic function at 6 months of follow-up.