Aim We aimed to evaluate impact of spironolactone (S) on cardiovascular toxicity of concomitant use of radiotherapy (RT) and trastuzumab (T). Background S, an aldosterone receptor antagonist, is known to ameliorate the cardiac damage. S ameliorates anthracycline -induced cardiotoxicity, there is no data regarding to effect of S on both T and radiation-induced cardiotoxicity. Materials/Methods Eighty rats were divided into eight groups: group (G) 1 was defined as control group. G2, G3 and G4 were RT, S and T groups respectively. G5, G6, G7 and G8 were RT + T, T + S, RT + S and RT + T + S groups respectively. Rats were sacrificed at 6th hour; 21st and 100th days after RT. Heart and thoracic aorta samples were taken for microscopical examination. Results Cardiac inflammation and fibrosis scores and; TGF-β expression were not significantly different within study groups at 6th hour and 21st days of RT. By 100th days of RT fibrosis scores and TGF-β expression in cardiac samples were significantly different between study groups (p values were 0.004 and 0.002 respectively). Pair-wise comparisons revealed that both cardiac fibrosis scores and TGF-β expression levels were higher in G5 when compared to G8 (p values were 0.046 and 0.028 respectively). Moreover the TGF-β expression was higher in G5 when compared to G2 (p = 0.046). We could not demonstrate any significant differences with respect to inflammation, fibrosis and TGF-β expression in thoracic aorta samples between study groups. Conclusions Although S had a protective effect on cardiac tissue it had no protective effect on thoracic aorta when administered with RT + T.