A case of enormous Chiari's network in a 7-year-old girl is described. It formed a parachute or spinnaker-like sack which moved freely into the pulmonary artery causing mild pulmonic stenosis. The preoperative diagnosis was believed to be myxoma of the right ventricle. The real condition was recognized during the operation. This is the seventh reported case of correction of so-called cor triatriatum dextrum.