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.
