A 40 year-old athletic woman presented with worsening dyspnea on exertion over the preceding several months. Chest radiograph showed borderline cardiomegaly and subsequent echocardiography demonstrated a 5.0-cm left atrial mass as well as left-to-right interatrial shunting through a patent foramen ovale. Cardiac magnetic resonance imaging was performed, which demonstrated signal characteristics consistent with an atrial myxoma. The patient then underwent urgent surgical treatment with good technical and clinical outcome. Histologic examination confirmed an atrial myxoma. Cardiac magnetic resonance imaging was valuable in characterizing the nature of the atrial mass and patent foramen ovale, helping guide the surgical approach.