Can you have a normal ekg and then have a heart attack then next day? or week later? i know they detect last or current heart attacks but what about an impending one?

Unfortunately, you can have a normal EKG and then have a heart attack the next day or a week later. An EKG can show ischemia, or low blood flow, which may be a warning of an impending issue but it doesn’t always show this and it can be normal before a heart attack. That is definitely a limitation of the test, even though it is very important to diagnose a heart attack that is currently happening

A normal ekg has no predictive value for a heart attack that might happen in the future. There are sometimes subtle changes or changes consistent with a previous infarct that might make it more likely in the future.