The premature P waves or PAC’s usually have a different morphology than the sinus P’s. A QRS usually follows a PAC and is usually identical to the patient’s normal complexes. Commonly, the P wave may not be conducted (or blocked). When a QRS is present, the PR is normal or prolonged. Isolated PAC’s are typically benign, but may be symptomatic and can provoke other atrial arrhythmias. The following animation illustrates what we have just described.