**Core Concept**
Atrial septal defects (ASDs) are a type of congenital heart defect characterized by an abnormal opening in the atrial septum, allowing blood to flow between the left and right atria. This can lead to increased volume load on the right heart, resulting in right ventricular enlargement and potentially pulmonary hypertension.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology and clinical presentation of ASDs. Patients with ASDs often present with signs of increased pulmonary blood flow, such as a prominent pulmonary component of the second heart sound (P2 > A2) and a fixed splitting of the second heart sound. The increased blood flow through the pulmonary valve can also lead to pulmonary hypertension, which can be a complication of untreated ASDs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ASDs are not typically associated with mitral valve prolapse. Mitral valve prolapse is a condition where the mitral valve leaflets do not close properly, allowing blood to flow backward into the left atrium.

**Option B:** This option is incorrect because ASDs are not typically associated with aortic regurgitation. Aortic regurgitation is a condition where the aortic valve does not close properly, allowing blood to flow backward into the left ventricle.

**Option C:** This option is incorrect because ASDs are not typically associated with aortic stenosis. Aortic stenosis is a condition where the aortic valve is narrowed, obstructing blood flow from the left ventricle to the aorta.

**Clinical Pearl / High-Yield Fact**
A key clinical finding in ASDs is the presence of a fixed splitting of the second heart sound, which is due to the increased pulmonary blood flow and pressure.

**Correct Answer: D.**