This ECG is from an 80-year-old lady who has collapsed or had sycopal episodes several times. The ECG comes from a Holter monitor. She has arterial hypertension and coronary artery disease. The ECG shows a second-degree, Mobitz Type II AV block. In both types of AVB, the PP intervals are usually the same. In second-degree AVB, Type I, the PQ (or PR) intervals progressively prolong until a P wave fails to produce a QRS.  The cycle repeats.  In second-degree AVB, Type II, the PQ intervals stay the same.  This is best identified by comparing the PQ intervals from just before the failed QRS and just after.  In Type II AVB, those two PQ intervals must remain the same.