We evaluated a 26yr old male with dyspnoea and clinical evidence of MS. To our surprise, echocardiographic evaluation revealed a primum ASD with normal function of the left and right atrioventricular (AV) valve. A left sided supra-valvular ridge or divided left atrium was identified with peak and mean gradients of 43/21mmHg respectively. The primum ASD was repaired with a pericardial patch and the supraventricular ridge causing left ventricular inflow obstruction was resected. The patient was discharged five days after surgery and has remained asymptomatic during routine follow up. Post-operative echocardiography revealed successful surgery with normal diastolic gradients of the left AV valve.