Well if you have a history of a Second Degree Type one A/V block (Mobitz, or Weinkebacke) Then you absolutely need to talk to your cardiologist. Which you already stated that you will be doing. There are a bunch of things that can cause this. The first thing that pops into my head is that your A/V block may by have moved lower down. Which could cause you to get a Second Degree Type 2 Block. If this happens then occasionally your heart rate will slow down to below your ventricles intrinsic rate. (intrinsic rate is the beats per minute that the pacemaker cells in a certain part of your heart will fire at it they do not receive frequent enough signals from pacemaker cells above them) In other words you got this block in the A/V node, which is the pacemaker between the atria and ventricles. If conduction system cells below the A/V node do not receive around 40 signals a minute then these cells assume that the pacemaker cells above them are not functioning and they start to fire on there on, causing the ventricles to contract at a rate of about 40 bpm. Once your A/V node starts functioning correctly the pacemaker cells will stop firing on there own. Does that make sense? I hope so cause that is about the best I can do, lol. Good Luck Buddy! ;-)