First degree AV block


  • Also known as first-degree heart block
  • Defined as prolongation of the PR interval on an electrocardiogram (ECG) to more than 200 msec (5 small squares on the ECG tracing)
  • Considered “marked” when the PR interval exceeds 300 msec (more than 7 small squares on the ECG tracing)

Clinical Features

  • Vast majority are asymptomatic and diagnosed by chance
  • Exercise may reveal decreased tolerance (especially when there is markedly prolonged PR interval and with left ventricular systolic dysfunction)

Differential Diagnosis

AV Blocks


First degree AV block


  • Asymptomatic patients do not require any specific management
  • Consider a cardiology consult for patients who may have symptoms attributable to the block (rare)


  • Outpatient

See Also

External Links