What Causes Shortness Of Breath?

I am a 53 yr old female, very healthy, thought I was, many years ago diagnosed with MVP, past year been have much shortness of breath, and heaviness in chest, went for my yearly exam, dr said he heard an s3 gallop, advised me to see cardiologist, dh has mentioned my regurgitation, I have been wearing cardionet monitor for 12 days now, 2 more to go, cardionet called dr on sat, thorn dr called me, said it showed flatline and some other events, cardiologist called me today, said it us not life threatening, but used the words, bundle branch and they moved my echo frim April 15th to this Wednesday. I am hoping after the echo I will know what is causing this shortness of breath and slight chest pain