ON THE COVER A 62-year-old man was diagnosed with an inferior ST-segment elevation myocardial infarction. Cardiac catheterization revealed severe 3-vessel coronary artery disease. Echocardiography revealed an ejection fraction of 40% to 45%. In the right ventricular inflow view, there was diastolic flow acceleration across the tricuspid valve with a possible extracardiac mass compressing this region. Cardiac computed tomography (CT) revealed a posteriorly displaced heart within the thorax (Panel A). There was interposition of lung tissue between the aorta and pulmonary artery, consistent with the diagnosis of congenital absence of the pericardium (Panel B). Cardiac magnetic resonance imaging (MRI) demonstrated that the heart was rotating freely within the patient's thorax (Panels C and D). The patient underwent successful angioplasty and stenting of all three coronary arteries. Image provided by Lyle N. W. Stronger, MD,* Robert McGregor, MD, FRCPC,† James W. Tam, MD, FRCPC,* Roger Philipp, MD, FRCPC,* and Davinder S. Jassal, MD, FRCPC*†‡ from the *Cardiology Division, Department of Cardiac Sciences, and †Radiology Department, St. Boniface General Hospital, and the ‡Institute of Cardiovascular Sciences, St. Boniface Research Centre, Winnipeg, Manitoba, Canada.

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