There are many different causes of heart failure (or weakening of the heart muscle). One cause of heart failure is coronary artery disease that leads to a heart attack at which point the heart muscle does not get enough blood supply and becomes weaker - this would be considered an ischemic cause (ischemia means limitation in blood supply). I recommend that you make an appointment with a cardiologist who will evaluation your heart function and help to diagnose the cause of heart failure if it is present.
http://my.clevelandclinic.org/heart/disorders/heartfailure/cardiomyopathy.aspx