A 17-year-old boy was assaulted by 3 men wielding baseball bats. Among multiple injuries, he sustained an injury to his left thorax (Fig. 1) with an associated pulmonary contusion but without pneumothorax or rib fractures. The patient's initial troponin I level of 1.35 ng/mL peaked 2 days later at 3.43 ng/mL. In addition, the initial electrocardiogram was markedly abnormal, with precordial R-wave and T-wave changes similar to those seen in apical hypertrophic cardiomyopathy (Fig. 2). A transthoracic echocardiogram revealed a left ventricular intramyocardial mass that extended from the mid lateral and apical lateral segments to the apex (Fig. 3). However, a diagnosis of left ventricular free-wall rupture with pseudoaneurysm formation could not be excluded. Cardiac magnetic resonance showed the intramyocardial location of the mass (Fig. 4). This finding, along with the history, was consistent with an intramyocardial hematoma from blunt chest trauma. While hospitalized, the patient remained hemodynamically stable without arrhythmias, and serial electrocardiograms showed decreasing T-wave inversions that did not completely resolve before the patient's discharge from the hospital. Ten months later, cardiac magnetic resonance showed that the intramyocardial mass had decreased in size (Fig. 5).