<prompt> Down syndrome is most commonly associated withASD with ostium secundumASD with ostium primumVSDTOF  <response>: An ostium primum atrial septal defect ASD occurs when then atrial septum near the atrioventricular valves has a communication between the two atrium causing a left to right shunt. The image to the right shows the location of the different types of atrial septal defects while looking from the right atrium. 1 Upper sinus venosus defect 2 Lower sinus venosus defect 3 Ostium secundum atrial septal defect 4 Coronary sinus atrial septal defect 5 Ostium Primum atrial septal defect Reference: GHAI Essential pediatrics, 8th edition 