A 44-year-old man was referred to hospital for the evaluation of atypical chest pain. His chest X-ray showed leftward displacement of the heart. During echocardiography, the apical window displaced laterally in the usual left lateral position and characteristic motions of the interventricular septum and left ventricular posterior wall were recognized with postural alterations. We presumed a complete absence of the left pericardium. Magnetic resonance imaging (MRI), however, demonstrated a partial left-sided pericardium. The diagnosis was corrected to partial absence of the left pericardium and we have carefully followed up this case without surgical prophylactic intervention. It is very important to differentiate partial from complete absence of the pericardium, because only in patients with partial absence of the pericardium is there a risk of fatal myocardial strangulation. The features of the chest X-ray and echocardiography of this case, which strongly suggested complete absence of the left pericardium, are possibly not always reliable signs. In cases with these abnormal imaging features, MRI may provide additional useful information, as in this case. (Circ J 2004; 68: 385 - 388)