Thrombolytic treatment to dissolve coronary artery blockage must be started within 3 hours of the onset of the episode?

More or less: The longer one waits after the onset of chest pain, the less likely that it is to help .Once the damage has been done to the heart, it is too late. The problem is that patients may have pain for longer periods of time before there is actual damage and there may be ongoing damage even if the pain started more than three hours ago. So this is often a difficult choice requiring a careful history.

Best results: May still work with higher disease or longer duration but with more risks.