24-Hour Holter Monitoring (often called a Holter monitor or 24-hour ECG) is a type of continuous cardiac monitoring that records your heart’s electrical activity—like a portable electrocardiogram (ECG/EKG)—for a full day while you go about your normal routine. Unlike a standard in-office ECG that captures only a few seconds, Holter monitoring tracks your heart rhythm continuously, which makes it especially useful for catching intermittent problems.

During the test, small adhesive electrodes are placed on your chest and connected by wires to a small recording device worn on a belt or shoulder strap. The monitor records each heartbeat and can detect changes such as:

• Heart rate patterns (too fast, too slow, or changing unexpectedly)
• Irregular rhythms (arrhythmias) including extra beats or pauses
• Rhythm changes that occur with activity, stress, or sleep
• Signs that may suggest reduced blood flow to the heart (in some cases)

Your results are reviewed by a clinician who analyzes the recording and matches any rhythm changes to the timing of your symptoms. In plain language, a “normal” result usually means your heart rhythm stayed within expected ranges and no concerning arrhythmia was captured during monitoring. An “abnormal” result may show episodes of an arrhythmia (for example, atrial fibrillation, supraventricular tachycardia, or pauses/blocks) that could explain symptoms like palpitations, dizziness, fainting, or shortness of breath. Because some rhythm problems are sporadic, a normal Holter test does not always rule out arrhythmia—it may simply mean it did not occur during that 24-hour period.

Clinicians commonly order 24-hour Holter monitoring when symptoms or prior findings suggest a possible rhythm problem that isn’t consistently present. It helps connect real-life symptoms to what your heart is doing at that exact time.

This test is often recommended if you have:

• Palpitations (a fluttering, pounding, “skipped beat,” or racing sensation)
• Unexplained dizziness or lightheadedness
• Fainting (syncope) or near-fainting
• Unexplained fatigue or reduced exercise tolerance
• Chest discomfort or shortness of breath when an arrhythmia is suspected
• A previously abnormal ECG that needs further evaluation

Holter monitoring is also used to support diagnosis and management in people with known heart conditions or risk factors, such as:

• Known arrhythmia (to measure how often it happens and how long it lasts)
• After starting or adjusting heart medications (to see if treatment is working or causing side effects like slow heart rate)
• After certain cardiac procedures (to check rhythm stability)
• Suspected heart rate variability issues during sleep or daily activities

Many providers ask you to keep a diary of activities and symptoms (for example: walking, climbing stairs, meals, stress, and sleep) and to note the exact time symptoms occur. This helps the care team correlate symptoms of heart disease with recorded rhythm changes and can guide next steps such as longer-term monitoring, imaging, blood tests, or treatment.

• Atrial fibrillation (AFib)
• Atrial flutter
• Supraventricular tachycardia (SVT)
• Ventricular ectopy (PVCs) and ventricular tachycardia
• Bradycardia (slow heart rate) and sinus node dysfunction (sick sinus syndrome)
• Atrioventricular (AV) block and other conduction disorders
• Premature atrial contractions (PACs)
• Ischemic heart disease/coronary artery disease (when rhythm changes suggest reduced blood flow)
• Cardiomyopathy and heart failure (arrhythmia assessment and rate control monitoring)
• Post–heart attack (post-myocardial infarction) rhythm monitoring

• Evaluating intermittent symptoms such as palpitations, dizziness, or near-fainting
• Detecting and characterizing arrhythmia to support diagnosis and treatment planning
• Monitoring overall heart health and day-to-day heart rhythm patterns
• Assessing how well rhythm or rate-control medications are working (and checking for side effects)
• Estimating arrhythmia burden (how frequently irregular beats occur over 24 hours)
• Guiding decisions about further cardiac monitoring (event monitor, patch monitor, implantable loop recorder) or specialist referral
• Supporting cardiovascular risk management by identifying rhythm issues that may affect stroke risk or heart function