Electrocardiographs, also known as ECGs, are medical devices used to record the electrical activity of the heart. There are a variety of synonyms for electrocardiographs, including cardiac monitors, EKG machines, heart monitors, and Holter monitors. Cardiac monitors are often used in critical care settings to continuously monitor a patient's heart rate and rhythm. EKG machines are commonly used in physician offices and hospitals to diagnose heart conditions such as arrhythmias and heart attacks. Heart monitors are portable devices that can be worn by a patient to monitor heart activity over an extended period of time. Holter monitors are also portable and are typically worn for 24-48 hours to collect continuous ECG data.