Apex: Opening Snap
The opening snap is a short, high frequency sound which occurs after the second heart sound in early diastole. It usually follows the second sound by about .06-.1 seconds. It is most frequently the result of the audible opening of the mitral valve due to stiffening (i.e. mitral stenosis) or increased flow (i.e. VSD, or PDA).
The opening snap is best heard between the apex and the llsb with the diaphragm of the chestpiece firmly pressed. During inspiration the opening snap of mitral origin is softer due to the decreased blood return to the left ventricle. With increased flow accross the tricuspid valve, as in ASD, a tricuspid opening snap may be heard, which is loudest at the llsb, and becomes louder with inspiration.