Objective: We report two cases (a girl with mitochon-drial disease and a boy with Noonan syndrome) who underwent growth hormone treatment for short statu-re. In both cases a hypertrophic cardiomyopathy was diagnosed. The girl was diagnosed at 7-years-old with growth hormone deficiency and she underwent sub-stitutive treatment for 5 years. A 15-old-age she was diagnosed with severe hypertrophic cardiomyopathy. Other clinical findings in this patient were: hypoacu-sis, pigmentary retinitis, muscular fatigue, mild neu-rological and intellectually delay. The patients presen-ted metabolic crisis characterized by abdominal pain, vomiting and lactic acidosis, so the diagnosis of mito-chondrial disease was established. Under the treatment with carnitine, Q10 coenzyme and beta-blockers, the evolution is stationary. The second case, a 14-years-old boy was diagnosed with Noonan syndrome and a pro-gressive hypertrophic cardiomyopathy was diagnosed after 2 years of treatment, so the therapy was ceased. The involvement of growth hormone therapy in aggra-vation of cardiac disease is highlighted in both cases.