Sure, there are other heart defects. A cardiologist may be able to tell from the location and sound of the murmur if it is TVD or something else.
The one that checked my TVD pup listened then said it was highly unlikely to be anything else but TVD, did we still want an echo? Well, we had the echo done anyway so the breeder would have confirmation of the diagnosis.
My general vet was not able to determine the exact problem just by listening. Have a cardiologist consultation to find out what you are dealing with. If you are near South Carolina go see Dr. Baumwart. That is who we went to, before he moved to SC.
Murmurs can be caused by any number of defects and can also be "innocent murmurs" that go away with age. Why worry and get gray hairs over it? You need a correct diagnosis and only a Cardiologist can do so. They may be able to do so with only an asculatation, which is a minimal fee (in our area $45 or so). If it is serious, regardless of cause, you may have to intervene surgically, or make an even tougher decision.
Make the appointment and make your decisions based upon what the cardiologist tells you.
As the Stage 3 murmur can be caused by a no. of different reasons including TVD, seeing a cardiologist as already stated would be the best, most knowledgable vet to work with. A cardio has many sized stethescopes and a 2d color echo Doppler.
I personally feel, most cardiologists will recommend a Doppler immediately after auscultation. Try to find a clinic near you or a little further, it's worth the ride for a proper diagnosis. I hope it's something minor and you'll be able to let out at sigh of relief.
