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First Degree Heart Block ECG Interpretation #316


  • First Degree Heart Block will look like a typical sinus rhythm with one distinguishing feature.
  • The P-R interval will be constant throughout the tracing and measure greater than 0.20 seconds.
  • Rate, regularity, P wave morphology and QRS duration and morphology will be unaffected.
  • NOTE: The rate will be that of the underlying rhythm. If the rate is “normal”, it will be 60 – 100 bpm. If it is bradycardia, the rate will be less than 60 bpm.
  • First Degree Heart Block is the most common heart block.
  • People are born with it every day. They will likely live a long and healthy life and die from some other malady.
  • Patients who develop a heart block during an MI bear close observation. This must be reported to the licensed healthcare practitioner immediately.


Notice the following: the only abnormality when analyzing this tracing is the abnormal duration of the P-R interval.

heart block ecg image 102

Practice Strip

heart block ecg image 103

Analyze this tracing using the five steps of rhythm analysis.

Show Answer
  • Rhythm: Regular
  • Rate: 68
  • P Wave: Upright
  • PR interval: 0.28 sec
  • QRS: 0.08 sec
  • Interpretation: First Degree Heart Block

Authors and Sources

Authors and Reviewers


? v:3 | onAr:0 | onPs:2 | tLb:0 | pv:1
uStat: False | db:0 | cc: | tar: False
| cDbLookup # 0

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