Paroxysmal atrial arrhythmias especially atrial fibrillation are frequently encountered in adult patients with atrial septal defect. However, the diagnosis of atrial defect can be difficult. Thransthoracic echocardiography, the mostly utilized cardiac technique, has shown a limited ability to identify small atrial defects. Transesophageal echocardiography has shown high accuracy to identify but it isn't well tolerated of the patients. Recently, the utility of multislice computed tomography in the evaluation of direction, location, and size of shunt flow in congenital heart disease has been demonstrated. Cardiac magnetic resonance imaging (MRI) is a recent imaging technique that permits with high spatial resolution and without ionising radiation an accurate identification of many cardiovascular diseases. We report an unusual detection of an atrial defect by phase-contrast cine MRI in a patient clinically suspected of arrhitmogenic right ventricular displasia.