[tgokh]

While a low reading on one of those meters (coupled with symptoms) is likely a good sign that something's wrong, I think it's quite possible for the pulse oximeter to read normal even if you're having a heart attack. There's a saying in medicine that "time is muscle" because the longer you wait to "fix" an obstruction in a coronary artery, the more likely that region of heart tissue is to die. However, tissue death is not (usually) sudden, so even if you're experiencing a significant heart attack, the heart may be pumping sufficiently and the lungs functioning normally to give you a normal oxygen reading

(this is not medical advice)