The differential diagnosis between pericardial and non-cardiac masses may be sometimes difficult in the evaluation of chest mass adjacent to the heart. One misdiagnosed case of non-cardiac mass as a pericardial mass turned out to be a hernia. When the contents of hernia originate from the gastrointestinal tract, the diagnosis is made easily by air-fluid shadow on plain chest roentgenogram. Morgagni hernia is usually detected on plain chest roentgenograms as a smooth, supradiaphragmatic shadow at the right pericardiophrenic angle. In the case of Morgagni hernia, in which the contents are only the omentum, it is necessary to differentiate the hernia from mediastinal fatty tumors. We report two cases of hiatal and Morgagni hernia containing omentum which were misdiagnosed as pericardial masses.