Please answer me. is a -3.1 mm st heart depression lasting longer than 1 minute bad or good?

Depends: It can be indicative of ischemia (inadequate circulation) but it depends on the morphology of the depression and the circumstances. For instance: 3 mm downsloping depression at peak exercise on a stress test associated with any degree of chest pressure is highly suggestive of blockage. 3 mm upsloping depression with no sx is non-specific, esp if the baseline ekg has non-specific changes also.