This Lead II rhythm strip was taken from a 12-Lead ECG performed on a 66-year-old man who was having an acute inferior wall M.I. The rhythm is normal sinus rhythm at 65 bpm. The QRS complex is slightly wide at 112 ms (.11 seconds). The patient did not have a bundle branch block pattern on his 12-lead ECG. The PR interval is .17 seconds, and the P waves are widened and have a "double peak". This can be a sign of left-sided heart failure, and is called P Mitrale. Your students should be advised not to try to diagnose acute M.I. from a monitor strip, as ST segments can be inaccurate on some types of monitors. However, any derangement of the ST segment on a monitor strip calls for an immediate 12-Lead ECG for confirmation.