An Intracardiac Mass in a Pediatric Patient

An 8-year-old boy was referred to the cardiology clinic for left ventricular hypertrophy on a routine electrocardiogram, performed as part of the work-up for attention deficit hyperactivity disorder. His parents report declining exercise tolerance and shortness of breath in the preceding year, a change from his previous asymptomatic baseline, but deny any other symptoms; vital signs were within normal limits and cardiac exam was unremarkable. An echocardiogram was performed, select clips of which are shown below.

Figure 1: Short Axis View

Figure 1

Which of the following represents the next best step for evaluation of the patient?

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