Silymarin is the main extract from the seeds of Milk thistle (Silybum marianum) and contains approximately 65-80% of silymarin flavonolignans compounds. The major component of the silymarin complex is silibinin. Cardiovascular toxicity is the leading cause of death associated with drugs overdose. The calcium (Ca2+)-binding protein S100B is a multifunctional protein primarily expressed by the brain and myocardial tissues, through its interaction with several effector proteins within cells have involved in the regulation of a variety of cellular processes such as protection from oxidative cell damage. This study was designed to investigate the cardioprotective effect of silymarin on clozapine-induced cardiotoxicity in albino Wistar rats. The heart damage was indicated by elevated levels of the plasma biomarkers such as S100B, troponin, and creatine kinase-MB (CK-MB). S100B levels were correlated with cardiovascular toxic effects induced by clozapine in a rat model. The results of this study showed that silymarin treated groups presented with significant difference in rat's weight and food consumption, compared to reduction in cardiotoxic groups. Plasma S100B levels were increased in cardiotoxic groups, declined in those treated by silymarin, and abolished by pretreatment with silymarin. Troponin I and CK-MB elevated significantly in cardiotoxic induced rats, which declined with silymarin treatment, and prevented in pretreatment by silymarin. The observed protective effects of silymarin in end organs, such as the heart, liver and Kidneys, against cardiotoxic agent clozapine were highly significant. The outcome of histopathological analysis of this study showed that the intensity of the evaluated parameters in cardiotoxic induced rats by clozapine was prevented in silymarin pretreatment which describe the cardioprotection by this agent. The correlation study presented with coefficient correlation between S100B and the studied parameters were significant positive correlation with troponin I and CK-MB. In conclusion, Silymarin significantly attenuated the cardiotoxicity induced by clozapine, and prevents the mediated damage to the heart. The efficacy of silymarin as cardioprotective agent explained by its mechanism of action as cardioprotective agent through anti-inflammatory, antioxidant, decrease S100B, troponin I, and CK-MB levels and correlated to each other.