Sinus venosus atrial septal defects (SV-ASD) have nonspecific clinical presentations and represent a diagnostic imaging challenge. Transthoracic echocardiography (TTE) remains the initial diagnostic imaging modality. However, detection rates have been as low as 12%. Transesophageal echocardiography (TEE) improves diagnostic accuracy though it may not detect commonly associated partial anomalous pulmonary venous return (PAPVR). Cardiac magnetic resonance (CMR) imaging provides a noninvasive, highly sensitive and specific imaging modality of SV-ASD. We describe a case of an adult male with exercise-induced, paroxysmal supraventricular tachycardia who presented with palpitations and dyspnea. Despite nondiagnostic imaging results on TTE, CMR proved to be instrumental in visualizing a hemodynamically significant SV-ASD with PAPVR that ultimately led to surgical correction.