If the cardiac infarct hasn't been clinically verified (or ruled out), no medical person in their right mind would recommend intense aerobic activity until a definitive diagnosis has been made...out of fear of extending the infarct even further.
One POSSIBLE exception would be if this possible infarct was an old event, and the person was not symptomatic. In such a situation, the doctor might order a stress
EKG to monitor how the patient's heart rate
responded to aerobic stress. But that would be done in a controlled situation with a medical team and resuscitative equipment on hand.