The size of the atrial septal defect can determine the amount of blood flow, and the amount of blood flow can also affect the progression of the disease. Persistent increased pulmonary artery flow can lead to pulmonary stasis, which in turn can lead to decreased vascular compliance and an increased volume load on the right heart, which over time can lead to organic pulmonary hypertension. The clinical manifestations of atrial septal defect are usually not obvious in childhood, but as the patient ages, he or she may develop characteristic exertional dyspnea with symptoms such as atrial fibrillation, atrial flutter, and ventricular arrhythmias. In addition, some patients may present with right heart failure, such as swelling of the lower extremities and hepatosplenomegaly. The most typical sign of atrial defect is a distinctive heart murmur that can be heard in the pulmonary valve area, i.e., a hyperactive second heart sound with a fixed split.