Prior to the development of CT, cardiac and pericardiac masses were evaluated by chest roentgenography, angiocardiography, and echocardiography. In most cases preoperative diagnosis of a specific entity was impossible. Preoperative CT diagnosis of an intrapericardial developmental mass becomes possible because of the presence of fat, fat/fluid level, thick walled cysts, as well as globular calcifications, bones, teeth, water density fluid, and soft tissue. A report of a young woman with a ruptured and infected intrapericardial teratoma and an infant with an intrapericardial bronchial cyst is presented.