Doxorubicin (DOX) is an anthracyclin antitumor antibiotic closely related to the natural product daunomycin. The most dangerous side effect of DOX is cardiomyopathy leading to congestive heart failure. This study aimed to investigate the cardiotoxicity of DOX by measuring lactate dehydrogenase (LDH), creatine kinase (CK-MB) enzymes, and troponin I level in serum, and measuring malondialdehyde (MDA) level in the heart muscle tissue. Sixty BALB/c male mice were used in this study. Except for mice in the control group, each mouse was implanted subcutaneously with 0.2 ml of the ascites fluid containing 1x106 Ehrlich carcinoma cells (ECCs) into the right thigh of the hind limb of a mouse. The total period of the experiment was 49 days (7 days before and 42 days after tumor inoculation). Mice were randomly divided into three groups (20 mice per each group) as follows: Group 1: Control group, in which mice received an intraperitoneal (i.p.) injection of 0.2 ml normal saline once weekly on days 0, 7, 14, 21 (for 21 days). Group 2: Solid Ehrlich carcinoma (SEC) control group, in which mice received an intraperitoneal injection of 0.2 ml normal saline once weekly on days 0, 7, 14, 21 (for 21 days) starting one hour after tumor inoculation. Group 3: DOX group, in which mice received DOX (4 mg/kg, i.p.) once weekly on days 0, 7, 14, 21 (for 21 days) starting one hour after tumor inoculation. The results of this study showed that, treatments with an intraperitoneal injection of DOX lead to increase of myocardial infarction markers as serum LDH, CK-MB enzyme activities, and Troponin I level. MDA increases in cardiac tissue homogenate in treated mice with DOX. It can be concluded that DOX treatment of male mice inoculated with SEC Tumor induced a myocardial infarction. Therefore, cancer patients treat with DOX should be checked the serum LDH, CK-MB enzyme activities, and Troponin I level during treatment to avoid myocardial infarction.