Yes an EKG can predict a heart attack and other heart diseases and heart problems.
The EKG measures your hearts electrical activity to see if it's beating properly and the EKG can detect whether you have abnormal heart activity and can detect heart disease as well as a potential heart attack.
Some EKG's show abnormalities which can be normal in your hearts rhythm however sometimes your hearts abnormal Rhythm shown on an EKG can signal a medical emergency, such as a myocardial infarction (heart attack) or a dangerous arrhythmia.