The presence of activating ras mutations in a cardiac leiomyosarcoma which occurred in the right atrium of the heart of a female patient was examined. The tumor had the appearance of leiomyosarcoma in rutine histopathological examination and the definite diagnosis was confirmed by a positive immunohistochemical reaction to smooth muscle actin. Molecular analysis by polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) technique showed a point mutation of H-ras gene at codon 12. To the best of our knowledge, this is the first report describing ras gene mutation in a cardiac leiomyosarcoma implying a role for the ras oncogenes in the development of this tumor.