Differential diagnosis
Mitral Stenosis must be distinguished from other conditions normally associated with a mid-diastolic murmurs such as Tricuspid Stenosis and Atrial Septal Defect. This should be possible given the other signs of MS; loud S1 and opening snap.

The opening snap may also be confused with the third heart sound indicating left ventricular falure. In LVF though, you would not normally expect any murmur to be present and the S1 should not be noticeably louder than normal.