Objective: The aim of the present study was to highlight on the effect of cardiotoxicity of Tilmicosin on dogs' health as well as the advantages of protective doses of antioxidants on the incidence of cardiotoxicity. Design: Experimental study Animals: Twenty adult Mongerl dogs Procedures: were divided into 4 groups each group consisted of five dogs, the first group was considered to be the control negative, the second group was treated with a single injection of tilmicosin, the third group was treated with L.carnitine followed by single injection of tilmicosin, the fourth group was treated with green tea followed by single injection of tilmicosin. Results: There was a continuous enlargement of the left ventricle (LVIDs) through the examination time in group 2, while there was transient enlargement in the left ventricle after 20 and 40 minutes in group 3. There was a significant increase in group 2, while there was a transient significant increase in group 3 after 40 minutes then become nonsignificant after 60 minutes. ESV results in all groups, there was a significant increase in group 2, while there was a transient significant increase in group 3 after 40 minutes then become non- significant after 60 minutes. There was a significant decrease in FS in group 2 more than both groups 3 and 4. Furthermore, there was a significant change by time, as it continued to decrease at 40 and 60 minutes. There was a significant decrease in EF in group 2 more than both groups no 3 and 4. Furthermore, there was a significant change by time, as it continued to decrease at 40 and 60 minutes. Conclusion and clinical relevance: The present investigation indicates that oxidative stress with alteration of antioxidant enzymes activities are feature of respiratory diseases in draft horses.