An EKG strip represents the electrical signal that passes through the heart muscle preceding a mechanical movement of the heart.
On a 12 lead EKG, the heart is observed from 12 different angles.
After an EKG strip is obtained, a doctor will look for any deviation from the normal electrical activity of the heart.
Most significantly, a doctor will typically look for ST segment elevation, indicative of myocardial infraction (also known as STEMI, or simply put, a heart attack).