The effects of cardiomyocyte grafting on left ventricular (LV) remodeling and function in rats with chronic myocardial infarction were evaluated using high-frequency ultrasound. Chronic myocardial infarction was induced in 50 Wister rats by ligating the left anterior descending artery. They were randomized into two groups: a trial group that received neonatal rat cardiomyocyte trans- plantation (n=25) and a control group which were given intramyocardial injection of culture medium (n=25). The left ventricular (LV) geometry and function were evaluated by high-frequency ultrasound before and 4 weeks after the cell transplantation. After the final evaluation, all rats were sacrificed for histological study. The results showed that 4 weeks after the cell transplantation, as compared with the control group, the LV end-systolic dimension, end-diastolic dimension, end-systolic volume and end-diastolic volume were significantly decreased and the LV anterior wall end-diastolic thickness, LV ejection fraction and fractional shortening were significantly increased in the trial group (P<0.01). Histological study showed that transplanted neonatal rat cardiomyocytes were found in all host hearts and identified by Brdu staining. It was suggested that transplantation of neonatal rat cardiomyocytes can reverse cardiac remodeling and improve heart function in chronic myocardial infarction rats. High-frequency ultrasound can be used as a reliable technique for the non-invasive evaluation of the effect of cardiomyocyte transplantation.