“A 12 lead EKG is a painless and noninvasive test that measures your heart’s electrical efficiency as it beats. As one of the fastest informational or diagnostic heart tests available, EKG testing can usually be completed in just five minutes.  To conduct an EKG test, our team attaches up to 12 small, flat, sticky patches called electrodes at various points on your chest, arms, and legs. The electrodes are connected to a monitor that registers your heart’s electrical activity over the course of the exam.Their is another device called telemetry monitoring that can be done in the hospital or even at home through what we call a holter monitor.  Both telemetry monitoring or holter monitoring are done with a 5 leads or electrodes on the upper chest (R and L side), mid chest (just under nipple line close to where the heart lies) and 2 more leads or electrodes just below the rib cage (on the R and L side). This holter device can be done for a couple of days and returned to the MD’s office.  An EKG or holter monitor test results that tell us whether electrical waves pass through your heart at a normal rate, faster than normal, slower than normal, or in an irregular pattern. Results that are fast, slow, or irregular, may be a sign that your heart is weak or overworked, or that it has some kind of structural (size or shape) abnormality.”

ECCA (https://eccacardiologists.com/2020/03/03/what-an-ekg-test-can-tell-your-doctor-about-your-heart/)