My Wife Is Being Treated For Multi Myeloma With Carfilzomib,

my wife is being treated for multi myeloma with carfilzomib, dexamethazone and Cytoxan. This latest regimen is after relapsing from treatment with velcaid and dexamethasone. She has recently developed difficulty breathing, most likely from the carfilzomib and or Cytoxan. We are concerned that this may be affecting her heart. She has had fluid removed from her lungs but still feels fatigued and thinks the fluid may be returning. An EKG turned up normal but we will do an Echo Cardiagram tomorrow as a precaution. Is it possible to have a normal EKG while showing some form of heart disease through the Echo Cardiagram? We are also looking to suspend this chemo regimen in favor of one with fewer side affects. Please advise.