Myocardial bridges are an unusual cardiac pathology in the study of chest pain in childhood. We present a 15 years-old patient with great arteries transposition surgically corrected which develops a supravalular pulmonary stenosis. A percutaneous pulmonary implantation is done successfully after coronary evaluation. Thirty six hours later, he presents clinic findings which seem coronary ischemia; consequently, we do a new cardiac catheterization in which we observe a myocardial bridge in anterior descendent coronary. Betablockers treatment is begun and clinic findings disappear. An increase preload of left ventricle after pulmonary valve implantation is suggested like a possible etiopathogeny.