- You will have your heart rate monitored by a Holter monitor. A Holter monitor is a machine that continuously records the heart's rhythms. Electrodes (small conducting patches) are stuck onto your chest and attached to a small recording monitor. You carry the Holter monitor in a pocket or in a small pouch worn around your neck or waist. The monitor is battery operated. After 24 hours, you return the monitor to the study doctor. The study doctor will look at the records and see if there have been any irregular heart rhythms.