low MUGA scan result

My recent MUGA scan showed ejection fraction of 44%. The one before 3 months was 54%. So I will not be getting Herceptin till my heart function improves, I am not sure when that is going to be. I am on Herceptin since March for Stage3b. I am very worried right now as I am considering Herceptin as my saftey net. I was under the impression that the heart problems due to Herceptin start to show up immediatly within 3 months and the longer you are on Herceptin the less likely you have a problem.
Now I am worried that even if I resume Herceptin after my heart becomes OK, what is the guarantee that it will not become bad again after continuing Hercpetin.
Anybody has any suggestions or experiences?

Thanks,
Julie