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###1: PR Interval

Published: August 9, 2026Updated: August 16, 2026

###3: The PR interval is an electrocardiogram (ECG or EKG) measurement that shows the time for an electrical impulse to travel through the atria, the heart’s upper chambers, and begin activating the ventricles.

Quick summary

["###4: The PR interval helps assess how electrical signals travel through the heart and can provide clues about certain rhythm or conduction abnormalities."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
8625-6
Short code
P-R interval
Synonyms
P-R interval
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ekg
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

###5: What the PR Interval Measures

###6: The PR interval is measured from the start of the P wave, which represents atrial depolarization, to the start of the QRS complex, which represents ventricular depolarization. It reflects the time required for the signal to pass through the atria, the atrioventricular node, and the His-Purkinje system.

###7: How the Test Is Performed

###8: An ECG is a quick, painless, noninvasive test. Small electrodes placed on the chest and limbs record the heart’s electrical activity, and a clinician or ECG system measures the PR interval.

###9: Why the Result Matters

###10: A prolonged PR interval may indicate delayed electrical conduction, such as first-degree atrioventricular block. A short PR interval can occur with certain rapid rhythms or conditions that allow electrical signals to bypass the atria normally, depending on the ECG pattern and clinical context.

###11: Factors That Can Affect the Result

###12: The PR interval can vary with heart rate, age, medication effects, electrolyte abnormalities, and other medical conditions. ECG findings are therefore interpreted by a healthcare professional together with symptoms, medical history, and the rest of the tracing.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

###13: The PR interval is not a laboratory blood test; it is a time measurement from an ECG. Its clinical significance depends on the overall ECG pattern and the person’s symptoms. An abnormal interval may prompt further evaluation, but it does not by itself establish a diagnosis.

Short name

###2: ECG PR interval

Frequently asked questions

###14: Does an abnormal PR interval mean that someone has a heart block?
###15: Not necessarily. A prolonged PR interval may be consistent with first-degree atrioventricular block, but other causes and the complete ECG must be considered. A short interval can reflect a different electrical pathway or rhythm and does not always indicate heart block.
###16: What symptoms may accompany an abnormal PR interval?
###17: Some people have no symptoms, while others may notice a slow, fast, irregular, or racing heartbeat, lightheadedness, fainting, chest discomfort, or shortness of breath. Seek urgent care for chest pain, severe shortness of breath, or fainting.
###18: Can medications affect the PR interval?
###19: Yes. Some medicines can slow or otherwise alter electrical conduction through the heart and lengthen the PR interval. Do not stop or change a prescribed medication without discussing it with a healthcare professional.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy