if you are looking for a "silent myocardial infarction" it means in non-medical jargon that a small part of the heart has suffered heart attack
and he or she is apparently coping well but is in for a rude surprise the next time it happens (it might not be silent the next time it strikes).
i believe it is also called silent ischemia
which simply means a loss of blood supply to a part of the heart, and one who has suffered an attack has barely noticed it.
according to wikipedia, "approximately one-third of all myocardial infarctions are silent, without chest pains or other symptoms."