We experienced a rare case of a patient with acute myocardial infarction. It was rare in that a piece of tissue, probably a remnant valve of the inferior vena cava in the right atrium, was dislodged by the Swan-Ganz catheter during a right heart catheterization study in the chronic phase of the disease. As far as we know, no other such case has been reported. Such remnants are considered to be present in 2 to 3% of the general population. Therefore, it is necessary to determine the presence or absence of a remnant before cardiac catheterization and to modify the procedure, such as by changing the catheter's approach, when a remnant is present.