Dr heard small murmur.went to cardiologist and echo/doppler was normal. he says its innocent. what about things it can miss, like subaortic stenosis? would the doppler have picked it up?

Echo is reliable: More likely than not the echo is correct and the murmur if present was an artifact.

Depends on Quality: As always, who has the most vested interest in your status & tests? Who should have their own copies of the data, including all the echo video images? A reasonably well performed echocardiogram should easily detect subaortic stenosis from the apical view on continuous wave doppler (ie. All velocities along the line of focus). Get & keep a copy of your images (& report) and examine carefully!

Hard to miss: A murmur is a noise the doctor hears when listening. They can be benign (from blood being ejected out) or more pathologic. A high quality echo study, preferably done in an accredited lab, should tell you what the murmur is from. It should not miss sub aortic stenosis. Good luck.

Yes: The echo is great about picking up things you mentioned. It is likely a pulmonary flow murmur. If you have no symptoms, you are probably fine, but if you have symptoms, especially with activity, you could consider asking for a "stress echo." hope this helped!