Heart problems other than ejection fraction while on herceptin?

[Paris]

I'm hoping someone will help me with this. I have had 12 herceptin treatments and my LVEF is improving (from 60% to 67%). However, lately I have been dealing with exercises intolerance. I get very short of breath while running and have had a couple of instances of strong heart palpitations while running. I also get very winded carrying things up stairs and experience on and off fatigue. In addition I have some mild edema which is different from the arm lymphedema I have. I saw a cardiologist who is going to do a stress echo and have me wear a holter monitor as well. He didn't have any answers because my symptoms don't show up when resting. I have mitral valve prolapse and have had palpitations previously but they were brought on by stress not physical exertion. My Mom died at age 50 of heart failure with no prior symptoms.

I am concerned because I have been on a consistent albeit easy running program since November and it has been a struggle to increase my endurance. It's like the oxygen can't get to my muscles the way it needs to. I have been active and in great physical shape my entire life. It is very frustrating.

I looked on the Genentech site but couldn't find any side effects listed that were similar to what I am experiencing. Maybe my body is still trying to recover from chemo?

Has anyone had this?

Many thanks!
Jamie