There are several different types of AV block:
-First degree, where the signal takes a little longer than normal to get from the atria to the ventricles but always does get through
-Mobitz 1/Wenckebach, where the signal gets delayed progressively longer until finally it doesn't get through (causing a skipped beat), and then this cycle repeats
-Mobitz 2, where the signal is delayed the same amount on every beat and then every few beats it doesn't get through
-2:1 etc. where for every 2 (or other number) signals from the atria only 1 (or other number smaller than the number of atrial signals) gets through to the ventricles
-Complete, where none of the signals from the atria get to the ventricles so the ventricles beat at their own slow backup rate that bears no relationship to that of the atria

As far as I know, the first two (first degree and Wenckebach, which are also generally not a big problem) are more common in athletes but I'm not so sure about the others. Which type are you asking about?