Two great resources for taking EKG practice exams online are ECG-Quiz.com and PracticalClinicalSkills.com. Both websites offer practice exams as well as instructional material for interpreting EKGs.
An electrocardiogram, typically abbreviated as ECG or EKG, is a graphical representation of the electrical activity of the heart over a defined time span. A conventional EKG uses a 12-lead EKG system, although only 10 actual leads are placed onto the body. The remaining two leads, called augmented leads, are derived using combinations of the other leads. The leads are essentially recording the activity of the heart from 12 different angles by measuring the electrical resistance between two leads.