Over twenty years ago, only those most progressive EMS agencies used 12-lead ECGs in the field. Since their implementation, the technology has progressed from a novel, cutting age nicety, to a standard of care, must have/must do assessment. The usage of the 12-lead ECG provides the rescuer with a clearer picture of the patient’s condition. In turn, this can be used to more quickly mobilize the needed teams into place at the specialty receiving hospitals which perform percutaneous coronary interventions (PCI treatments) and open-heart surgery. The saying, time is muscle, is well known to those treating patients with ST-segment elevated myocardial infarctions, or STEMIs. By using prehospital 12-leads, and transmitting this data or otherwise alerting the receiving facility to the findings in the field, there has been a marked decrease in the EMS-to-balloon times in STEMI patients. What was beneficial two decades ago is fundamental now. For the new student, this course will serve as an introduction into the interpretation of an ECG and will include the following aspects: electrode placement and ECG leads, the autonomic nervous system, automaticity, methods of determining the heart rate and regularity of rhythm on an ECG, and a “putting it all together lesson”. For the more experienced learner, it serves as a refresher reinforcing the basics of the assessment.