Yes, "Heart Disease" is a generalized or generic term for "problems of (or related to) the heart", but it is never a diagnosis just as the term "Mental Illness" does not indicate whatever might actually be wrong. My own "Heart Disease" has to do with blockages in arteries around or near the heart even though my heart, itself, is just fine. In the same regard, the term "Mental Illness" does not in any way identify any actual problem.