Longhorn,
Are they monitoring your heart? If not, make sure they start immediately. My husband did develop extreme shortness of breath while on Nexavar. He was diagnosed with congestive heart failure and had to stop the Nexavar. I don't know for a fact that it was caused by the Nexavar (his onc says it wasn't, but she never seems willing to admit that her treatments can cause problems). But I do know that they are seeing heart issues with Sutent which is similar to Nexavar. He is now on heart medication that is controlling that issue quite well and moved on to Torisel.