Secundum ASD or ostium secundum atrial septal defect 

In this case, using cardiac CT the size of the ASD could be accurately measured (1.7 cm).

During respiratory inspiration, the negative intrathoracic pressure causes increased blood return into the right side of the heart. The shunting of blood from the left atrium to the right results in volume overloading of the right heart, resulting in an enlarged right ventricle.

Most individuals with an uncorrected secundum ASD don't have significant symptoms through early adulthood. About 70% develop symptoms by the time they are in their 40s. These patients will present with symptoms of dyspnea on exertion (shortness of breath with minimal exercise), congestive heart failure, or cerebrovascular accident(stroke).