This patient most likely has a bicuspid aortic valve. Bicuspid aortic valve is the most common congenital heart lesion, occurring in approximately 0.5% to 2% of the general population. It is the second most common cause of aortic stenosis after calcific degeneration of a tricuspid aortic valve and the second most common cause of aortic regurgitation after aortic root dilation. Many patients with a bicuspid aortic valve are asymptomatic, with the diagnosis being suggested based on incidentally noted auscultatory findings. The presenting murmur depends on the degree of valve dysfunction, with a systolic ejection murmur that varies in intensity, ranging from minimal flow disturbance to findings consistent with the murmur of aortic stenosis as the degree of outflow obstruction increases. A diastolic murmur may occur if aortic valve incompetence with regurgitation is present, as in this patient. Bicuspid aortic valve has an increased prevalence associated with congenital lesions such as aortic coarctation, interrupted aortic arch, and Turner syndrome. More than 70% of patients with a bicuspid aortic valve will require surgical intervention for a stenotic or regurgitant valve or aortic pathology over the course of a lifetime. The presence of a bicuspid aortic valve increases the risk for aortic stenosis or regurgitation, and stenosis proceeds at a faster rate when the aortic valve is bicuspid. The risk for infective endocarditis also is increased in these patients. In addition, bicuspid aortic valve is associated with aortopathy and a predisposition to aneurysm formation and thoracic aortic dissection.

Adults with previously undiagnosed aortic coarctation may present with hypertension or a murmur. Palpation of reduced femoral pulses and measurement of discrepant blood pressures during routine examination are helpful in raising suspicion for the diagnosis. The murmur associated with coarctation may be nonspecific but is usually a systolic murmur in the left infraclavicular area and under the left scapula.

The murmur associated with an atrial septal defect is a midsystolic flow murmur caused by the ejection of increased right-sided volume, owing to the left-to-right shunt that occurs initially with this defect. This murmur is best heard over the pulmonic area of the chest and may radiate toward the back, as with the murmur of pulmonary stenosis. The most characteristic finding on auscultation in patients with an atrial septal defect is a fixed split S₂.

The murmur of mitral stenosis is a diastolic low-pitched decrescendo murmur heard best in the left lateral decubitus position. With mitral stenosis, S₁ has increased intensity and S₂ is normal. The opening snap, which is due to forceful opening of the mitral valve, occurs when the pressure in the left atrium is greater than the pressure in the left ventricle. As the severity of the mitral stenosis increases, the pressure in the left atrium increases, and the mitral valve opens earlier in ventricular diastole.