Holter is a test with which we can record the electrocardiogram (ECG) continuously through a portable device for 24 to 48 hours. The device is connected to the patient’s chest with electrodes. The electrocardiogram is recorded while the patient performs his usual daily activities. The data are then analyzed by the doctor in order to recognize any electrocardiographic abnormalities. 

It is mainly used for the diagnosis of arrhythmias, especially in cases of symptoms like palpitations which occur occasionally and are not evident on a regular visit to the doctor.