occlusion of the right
coronary artery is responsible for most infarcts involving the posterior and basal
portions of left ventricle.

occlusion of more proximal
segments of the coronary arteries products larger infarcts involving the full
thickness of myocardium

occlusion of more distal arterial branches cause large zone of infarcts,

long standing coronary atherosclerosis, collateral circulation
may develop over time in response to chronic ischemia, this collateral increase the size
of infarct.

with M.I for the first 18 hours no changes
are evident on gross examination ,

Microscopically: Coagulative necrosis become apparent by about 12 to 18 hours in MI

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