The association of tetralogy of Fallot with atrial isomerism has been rarely reported. Eight cases (five with left isomerism and three with right isomerism) are known. This paper reports two other cases of tetralogy of Fallot with left atrial isomerism. The syndrome's defects were disguised and without clinical expression because of the presence of the right ventricular outlet obstruction of tetralogy of Fallot. These diagnostic elements, not recognized in one of the patients previous to surgical correction of tetralogy of Fallot, were present: junctional rhythm, bronchial isomerism, partial anomalous pulmonary vein connection, agenesy of inferior vena cava and abdominal heterotaxy; their identification previous to surgical correction of tetralogy of Fallot, is necessary for an adequate surgical management.