Background: Despite worldwide use of monosodium glutamate (MSG) as a flavor enhancer, its consumption has been an alarm due to daily exposure without definitive safety or exact limit. Vitamin C has an antioxidant activity. Objective: to clarify effects of neonatal MSG intake on heart structure of male albino rat pups and the possible modifying role of vitamin C and to assess reversibility of these effects. Material and Methods: 40 male albino rats at postnatal day 1(PD1) were allocated to three groups; control, group B administered MSG (4 mg/gm bw/day) and group C administered previous dose of MSG plus vitamin C (500 mg/kg bw/day) for 10 days. Groups B and C were subdivided according to animal sacrification age into B1, C1 sacrificed at PD10 (after the last dose of treatment) and B2, C2 sacrificed at PD30 (20 days after treatment cessation). At experimental end, left ventricular specimens were processed for histopathological, immunohistochemical and morphometric studies. The Results: Histologically, group B1 revealed massive degenerative changes including marked muscle fibers disruption, degeneration, separation with increased CT cells and fibroblasts, dilated congested capillaries and extravasated hemorrhage. Cardiomyocytes showed nuclear pyknosis, cytoplasmic coagulative necrosis and vacuolation. Previous changes were still present in group B2 but with less degree. MSG plus vitamin C resulted in greatly restored normal cardiomyocyte architecture in group C1 but complete recovery was observed in group C2. The mean area percentage of collagen fibers, vimentin and iNOS expressions showed high significant increase in B1, B2, low significant elevation in C1 but non-significantly different in C2 relative to control group. Conclusion: MSG induced myocardial toxicity in early postnatal period. Vitamin C greatly ameliorated histopathological and immunohistochemical alterations in cardiac tissue. MSG withdrawal for 20 days showed mild improvement but withdrawal after vitamin C administration was more effective in reversibility of MSG toxicity.