There's no way a normal ECG could predict that- ECGs only show how the heart is doing at that particular instant. A normal ECG cannot predict future heart function. You might perform an ECG which comes back normal, and then minutes later the patient has a heart attack.
Though if an ECG is abnormal it does make having a heart attack or another cardiovascular event (such as stroke) much more likely and these people would likely be put on some form of treatment.
Such things an ECG might show up are arrythmias (abnormal heart rythyms), changes in the heart shape (such as enlarged heart in heart failure), ECGs can show previous heart attacks as well as angina and conduction problems within the heart (heart blocks). All of which can be treated and hopefully prevent a heart attack in the future.
