From the Guidelines

The murmur associated with aortic regurgitation is typically a high-pitched, decrescendo diastolic murmur.

The murmur begins with or shortly after the second heart sound (S2)
It is usually best heard at the third and fourth left intercostal spaces, but can be louder in the right intercostal spaces if the regurgitation is due to aortic root dilatation 1
The murmur can be accompanied by other physical findings such as a wide pulse pressure and characteristic peripheral findings that reflect the wide pulse pressure 1
In severe cases, an Austin-Flint rumble may be present, which is a low-pitched, rumbling diastolic murmur heard at the left ventricular apex 1

The intensity of the murmur can be affected by various factors such as respiration, position, and exercise 1
The murmur can also be affected by pharmacological interventions such as amyl nitrite inhalation, which can decrease the intensity of the murmur 1

The diagnosis of aortic regurgitation can be made based on the physical examination findings, including the characteristic murmur, as well as other diagnostic tests such as echocardiography 1
Echocardiography can provide a semiquantitative estimate of the severity of the regurgitation, as well as assess the cause of the regurgitation and the valve morphology 1

From the Research

The characteristics of the murmur associated with aortic regurgitation can be described as follows:

A diastolic murmur is typically associated with aortic regurgitation, but systolic murmurs can also be present 2, 3
The presence and severity of the murmur can vary depending on the severity of the aortic regurgitation 2, 3
A systolic murmur can be a common presentation of aortic regurgitation, especially in patients with mild or moderate disease 3
Diastolic murmurs are more commonly associated with severe aortic regurgitation 2, 4
The murmur can be characterized by a bisferious pulse contour, which is a pattern of two systolic peaks, and diastolic reversal of flow direction 5

The determinants of the murmur associated with aortic regurgitation include:

Peak aortic flow velocity, which is a significant determinant of systolic murmur 2
High grade aortic regurgitation, low diastolic blood pressure, high peak velocity of the AR jet, and high systolic blood pressure, which are significant determinants of diastolic murmur 2
Severity of aortic regurgitation, which can affect the presence and severity of the murmur 2, 3

The clinical significance of the murmur associated with aortic regurgitation includes:

The murmur can be a clue to previously unsuspected cardiovascular disease, especially in patients without a detectable murmur 5
The presence and severity of the murmur can guide patient management and optimize timing for intervention 6
Echocardiography is key for imaging the aortic valve morphology and flow, as well as aortic root and ascending aorta, and determining LV ejection fraction and dimensions 6