This ECG shows a nice, clear atrial flutter with 4:1 conduction. Also, there are frequent PVCs. Good for students who have mastered the criteria for the basic arrythmias and who need to see combinations. That is, PVCs are not only seen with NSR, and it is important to state the underlying rhythm. For your more advanced students who understand how to plot frontal plane axis, the axis of the PVCs is nearly straight up - a very strong argument for the ventricular origin of the beats.