<prompt> Most common type of Atrial septal defect is:Ostium primumOstium secondomEndocardial cushion defectEndocardial hypertrophy  <response>: Ostium secondum 400-G 401-Ghai 7thAtrial septal defect - ostium secondum type is 10 times more common than the endocardial cushion defrct. Ostium secondum - generally anatomically located at the fossa ovalis superior or posterior to the fossa - ovalis. Ostium primum - is situated inferior to the fossa-ovalis CHF, Infective endocarditis is rare The ideal age of operation is between 2-5 years. 