Good Lord, lily,
JUST THIS WEEKEND? Or did you get that year wrong?
I'm going to assume you meant 2005. To be honest, I don't know exactly how it is measured, my guess is that it isn't precisely.
What IS important is the remaining heart function becasue after a heart attack or series of heart attacks the heart efventually progresses towards heart failure which is the progressive weakening of the heart best reflected in the ejection fraction.
If a sizeable portion of the heart is killed, an echo will show an area that doesn't contribute to proper beating resulting in a "floppy" looking beat...but I don't think they can quantify too precisely from that how much heart has died.
That's maybe why it seems doctors are stuck with only two words: "minimal" and "massive."
(I'm glad you got the "minimal" version.)
Have they measured your Ejection Fraction?