MI symptoms and Nitroglycerin

I'm going through Pathoma and noticed it says nitroglycerin doesn't relieve MI symptoms (chest pain, left arm or jaw pain, diaphoresis, dyspnea), although later on, it's mentioned that nitrates are a possible treatment for MI. Can someone please explain this discrepancy to me please? Thanks fam
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums