Histopathological diagnosis was used to understand the pathological events associated with Heterophyes heterophyes (H. heterophyes) infection. CD3 and CD79α antibodies had been used as markers for both T and B lymphocytes respectively. Immunohistochemical techniques had several advantages as remarkable sensitivity and specificity. This study aims to evaluate the roles of praziquantel (PZQ) and aminoguanidine (AG) treatment in H. heterophyes infected dogs pathologically and immunohistochemically. Study design included experimental infection of dogs with encysted metacercariae of H. heterophyes followed by treatment with PZQ and AG. Tissue samples were taken from small intestinal, liver, heart and lung of all groups for histopathological and immunohistochemical studies. Pathological changes were detected in infected tissues by histopathological examination. There was different degree of CD79α+B lymphocytic & CD3+T lymphocytic infiltration detected in immuno-histochemical stained tissues. PZQ caused improvement of pathological changes in the small intestine. However the cellular inflammatory infiltration increased. There was reduction in inflammatory infiltration after intake of AG. Both PZQ and AG improved the pathological changes in the liver, heart and
lung, while the cellular inflammatory infiltration increased after PZQ and reduced by AG. Moreover in the lung AG improves pulmonary congestion and alveolar wall thickness.