Following Is true regarding opening snap -

The high pitched opening snap (OS) of MS occurs after a very sho interval after the second hea sound. The opening snap (OS) of the mitral valve is most readily audible in expiration at, or just medial to, the cardiac apex. This sound generally follows the sound of aoic valve closure (A 2 ) by 0.05-0.12 s. The time interval between A 2 and OS varies inversely with the severity of the MS. The OS is followed by a low-pitched, rumbling, diastolic murmur, heard best at the apex with the patient in the left lateral recumbent position. In general, the duration of this murmur correlates with the severity of the stenosis in patients with preserved CO. ( Harrison&;s principle of internal medicine,18th edition,pg no. 1931 )