If we say a heart attack is the point at which a person begins to experience chest pain, approximately how long the heart muscles is denied oxygen might that be?

 

For the sake of theory, let's assume the artery isn't blocked gradually; it was open, then it's closed.

I do not think that one can reasonably assess that. Many heart attacks are not associated with pain, for example http://www.nhlbi.nih.gov/health/health-topics/topics/heartattack/signs.html

there's a lot to type, so i'll refer you to this link,

 

http://www.heart.org/HEARTORG/Conditions/HeartAttack/Heart-Attack_UCM_001092_SubHomePage.jsp