الفهرس 
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Abstract
Introduction : Stress is an unpleasant state that changes the physiological homeostasis and the balance of organisms and leads to long-term pathological changes in a variety of systems like the digestive, circulatory and neuroendocrine systems. Animals and methods :This work was carried out on twenty four adult male albino rats. They were divided into three groups of eight rats each i.e. control group, stress group and recovery group. Animals of all groups were sacrificed at the end of the experiment. The anterior thoracic wall was incised bilaterally and the heart was exposed, removed, washed with purified buffered saline. Heart was sectioned into four transverse slices from the apex to the base parallel to the atrioventricular ring then each slice of the myocardium was soaked in 10% formalin solution for 48 hours, dehydrated in graded alcohol series, and then embedded in paraffin wax. Paraffin sections were prepared and stained with haematoxylin & eosin, Nestin and vascular endothelial growth factor (VEGF) stains. Results : Microscopic examination of the hematoxylin and eosin slides revealed the presence of structural changes in the heart tissues, which were confirmed by the presence of a statistically significant increase in the stress histological index in the stress group compared to the recovery and control groups. The microscopic examination of Masson slides showed that there are more fibrous tissues in the stress group than the recovery and control groups. The immunohistochemical study showed the presence of nestin positive cells and expression of VEGF in the heart muscle of the stress group more than the recovery and control groups. These results were confirmed by the presence of a statistically significant increase in the optical density of the two immune stains in the stress group compared to the other two groups.. Conclusion: chronic stress may be responsible for histological and immunohistochemical changes that occur in the heart muscle of albino rats.