Atrial septal defect (ASD) diagnosis starts with a physical exam listening for a heart murmur, followed by imaging tests like an echocardiogram to visualize the heart's structure and blood flow, which is the main diagnostic tool. Additional tests may include a chest X-ray to see the heart and lungs, an electrocardiogram (ECG) to record the heart's electrical activity, or more advanced imaging such as a cardiac MRI or CT scan if the diagnosis is unclear. Physical Examination