Cardiovascular lesions are considered as one of the most important factors leading to mortality of rainbow trouts in different breading system. The aim of this study was to compare the extent and the intensity of occurrence of pathologic lesions in the heart and BULBUS ARTERIOSUS of rainbow trouts in extensive, semi intensive and intensive cultivation systems. For this purpose, 10 fish specimens from 7 weight groups (less than 90 grams, 90 to 300 grams, 300 to 500 grams, 500 to 1000 grams, 1 to 3 kilograms, 3 to 5 kilograms and over 5 kilograms) and a total of 210 specimens were collected randomly from 3 farms in Haraz and Espiran regions and their heart and BULBUS ARTERIOSUS collected. In field research, age, sex, mortality rate, stocking density, feeding type and the physical and chemical specifications of the water were also taken into consideration. Histopathological slides were prepared from the collected specimens and stained with Hematoxylen and Eosin. Histopathologically, 47 male and 73 female fish had cardiovascular injuries with 29 cases in extensive cultivation system, 41 in semi intensive and 50 in intensive systems. Edema and hyperemia in the spongy layer of the atrial and ventricular muscles, moderate to severe muscular degeneration, moderate to severe inflammation, mild to severe vascular damage, thrombus formation, necrosis and fibrosis were the most important pathologic changes observed. The severity of lesions increased with increasing age of the fish in all three cultivation systems. The extent and intensity of pathologic lesions in fish over 500 grams was completely significant (p<0.05). These changes were significant in intensive cultivation system compared to the other two system (p<0.05). There was also significant difference between male and females (p<0.05).