This was taken from the web site below. Read the article to understand more. Generally, your mom is on the lower end of the scale, but nothing to be majorly concerned about at this point. I am sure her onc will continue to monitor her heart. At some point he/she may decide to give her a "vacation" so that her heart can get strong again.
>In general, most incredibly fit people are often in the 70s while "regular" people are in the high 50s and in the 60s. It is very rare for oncologists to give additional chemotherapy containing anthracylines (the chemotherapeutic agents mentioned above) or Herceptin if the LVEF goes much below 50, except in unusual situations. <
http://www.yana.org/herceptininteractions.htm