Pheochromocytoma is a rare tumor of childhood, arising from adrenal medullary and chromaffin tissue. Because chronic hypoxia may induce pheochromocytoma, there have been several reports of pheochromocytoma development in cyanotic patients after corrective or palliative cardiac surgery. The variable clinical presentation of pheochromocytoma is obscured by both underlying heart disease and medications. If sudden hypertension, aggravation of a heart condition, or unusual symptoms such as diabetes mellitus develops in a cyanotic patient with congenital heart disease, pheochromocytoma must be ruled out. We report two patients presenting with cyanotic single-ventricle heart disease with pheochromocytoma.