Inflammatory myofibroblastic tumor (IMT) or inflammatory pseudotumor is a rare primary cardiac tumor that may result in sudden death. We report a sudden unexpected death due to occlusion of the coronary arteries by IMT arising from the left coronary cusp of the aortic valve. An 8-year-old child suddenly woke up from his sleep with complaint of severe chest pain to his parents, and shortly he became unresponsive. He expired 40 min later in the hospital despite resuscitation efforts. The postmortem examination revealed a 2.5 × 2 × 1-cm mass composed of multiple entangled slender cylindrical fronts, filling the coronary sinus and obstructing the coronary ostia. The patient had complained of recurrent chest pains about 2 weeks prior to his death. Echocardiogram was conducted on the patient but did not recognize the mass. Histological examination of the mass established the diagnosis of primary cardiac IMT. The detailed pathological findings are described. In addition, the literature is reviewed, and pathogenesis, clinical presentation, and the importance of forensic autopsy examination are discussed.