Introduction. Isaacs' syndrome is a disorder of unknown etiology characterized by muscular rigidity, cramps and myokymias. Described by Isaacs in 1961 and called by him as continuous muscular activity syndrome. There are few reports in Latinoamerican countries. Clinical case. A 31 year-old man with sustained muscular contractions in lower limbs and diffuse myokymias since he was eighteen year-old. Dextrocardia was disclosed on clinical examination. Conclusions. We report the case of a patient with Isaacs' syndrome and dextrocardia.