An electrocardiogram (ECG or EKG) is a test that checks how your heart is functioning by measuring the electrical activity of the heart.
A standard echocardiogram (echo), is an imaging technology that uses ultrasound to create images of your heart. It is a diagnostic test used to examine the heart and its blood supply, determine how large the heart is, how well it contracts, and how the valves function.
Holter monitoring is primarily an outpatient test. The holter monitor is worn by the patient for 24/48/72 hours. The heart's rhythm is recorded electronically on the device during this time. It is later scanned by the cardiology technologist and reviewed by an internist.