Memory loop monitoring is the process of recording the heartbeat over a longer period of time, up to 30 days. The longer it is worn, the greater the chances of capturing the event.

While the Holter has a 24-hour tape that is scanned for cardiac arrhythmias, the memory loop recorder has a relatively small amount of memory, perhaps only 5 – 30 minutes total.  Some memory loop recorders have only one memory bank, while others have multiple memory banks. The first memory bank is the most useful and often all that is needed.

When the patient is connected to the memory loop recorder, its memory bank starts filling with ECG data. Typically this bank can store 2-3 minutes of memory, so it takes 2-3 minutes to fill. Once filled, for every new heartbeat that comes in, the memory loop recorder throws away the oldest one in memory because it's no longer needed.

This is called a moving window of ECG data. When the patient feels something strange and pushes the symptom button, the last 2 minutes of memory data are frozen in memory. This memory data can now be transmitted to a central receiving center via a standard telephone. Since the data is frozen in memory, it is not critical that you rush to the phone. Get there quickly but safely.

Some recorders are equipped with 2 or more additional memory banks, which means that if you have a second or third symptom on the way to the phone, you can push the symptom button again to capture the new events. These are handy but not mandatory. Some memory loop recorders can programmed to record events up to 5 minutes or more.