What is a Holter Monitor and What Can it Detect?
By Dr Nabila Laskar — published March 2025.
A comprehensive guide to 7-day heart monitoring and how it helps diagnose palpitations, dizzy spells and arrhythmias.
What is a Holter Monitor?
A Holter monitor is a small, portable device that continuously records the heart's electrical activity (ECG) for typically 7 days. Unlike a standard ECG that captures 10 seconds, a Holter records every heartbeat — dramatically increasing the chance of capturing irregular rhythms that occur sporadically.
Why 7 Days Instead of 24 Hours?
Extending monitoring from 24 hours to 7 days significantly improves diagnostic yield. 24-hour monitoring detects arrhythmias in approximately 40% of patients; 7-day monitoring in approximately 85%. The longer window captures variation across the week including weekend activities, sleep and different stress levels.
What Can a Holter Monitor Detect?
Common arrhythmias detected include atrial fibrillation (AF), supraventricular tachycardia (SVT), ventricular ectopics, heart block and bradycardia. The recording also lets us correlate symptoms with rhythm at the exact moment, identify silent arrhythmias, assess heart rate variability, evaluate pauses during sleep, and monitor response to medication.
What to Expect
Application takes about 5 minutes — small adhesive electrodes are placed on the chest and connected to a lightweight recorder worn discreetly. You continue normal activities for 7 days, keeping a brief symptom diary. After returning the device, specialist software and a cardiologist analyse over 600,000 heartbeats and correlate findings with your diary, with a written report following.
Practical Considerations
The device must stay dry, so quick waterproofed showers or bed baths are recommended. Impact on daily life is minimal — most patients forget they are wearing it after the first day. Normal exercise is encouraged, as it may trigger the symptoms we are trying to capture, and the device can be worn at work.
When to Consider Holter Monitoring
Holter monitoring is particularly valuable for palpitations, episodes of dizziness or lightheadedness, unexplained fainting, unclear shortness of breath, chest discomfort related to activity or stress, and follow-up after treatment for known arrhythmias.
Related reading
See our patient guides to Atrial Fibrillation and Heart Palpitations, the two conditions most commonly investigated with a Holter monitor.