We examined a 26-year-old female with a dilated right heart without significant valvular disease. The first transthoracic echocardiography (TTE) did not identify any intracardiac left to right shunt diseases. A contrast-enhanced computed tomography scan showed a sinus-venous atrial septal defect (ASD) and partial anomalous pulmonary venous connection. A superior sinus-venous ASD at the ceiling of atrial septum and two anomalous pulmonary veins connected to the superior vena cava and to the right atrium, respectively, were visualized on the second TTE. Three-dimensional anatomical understanding from multiple imaging modalities may occasionally necessary to delineate rare congenital heart diseases by echocardiography, particularly in adult with a limited echo window.