ules.... Don't panic. I worked with several ATCOs at Heathrow (one of whom was an ATPL holder too) who had bundle branch blocks. They were as fit as anything. I had an ECG "problem" too, but was told it was the way I was wired up, and I used to run the 7 floors up to the top of Heathrow Tower and beat the lift!. Good chance you'll be OK so look on the bright side. The medics are very picky but simply want to find the reason, then they'll be happy.