What are ekg's for?

Electrical activity. Electrical activity of the heart can evaluate heart rate, rhythm, health of conduction tissue in the heart and also clue one nto other heart diseases such as ischemia, hypertrophy, enlarged heart and cardiomyopathy. An ekg referrs to a tracing of such electrical activity from multiple vectors.
Heart evaluation. An EKG (also more properly known as an ecg) is an electrical tracing of your heart in 12 different positions ("12 lead ecg"). It is used to determine the the history and health of your heart.