This rhythm strip shows sinus rhythm with frequent premature atrial complexes. The characteristic features demonstrated here include: an underlying normal sinus mechanisms with normal P waves preceding each QRS and frequent early or premature P waves followed by early QRS complexes. The premature P waves most often differ in shape from the sinus P waves. In this case, some of the early P waves are partially superimposed on the preceding T wave. The premature QRS complexes are conducted normally.