This rhythm strip shows sinus rhythm with conducted premature atrial complexes (PACs). The characteristic features demonstrated here include an underlying regular rhythm with sinus P waves preceding each on time QRS complex. Two early or premature P waves are each followed by premature QRS complexes.

As is usual, the premature P wave morphology is different from that of the sinus P waves, while the premature QRS complex morphology is similar to that of the sinus beat.

PACs may be non conducted and are a common cause for sinus pauses when there is sinus node resetting and overdrive suppression. Like all premature beats, PACs per se do not identify heart disease and are most often benign.