From my experience the FAA class 3 is passable by demonstrating you are breathing.
That's far from actually true, but a lot of people do believe it.
I was at one FAA aviation lawyer's presentation and a member of the audience (a "security orificer" at some UK airport) stood up and had a good old rant that they have a UK licensed pilot there who got a heart attack but continued to fly on an FAA license.
Anybody who knows the detail knows this is disingenuous nonsense. The FAA will ground you just the same, and both will let you fly, noncommercially, after various requirements are met, which takes about 6 months. And on renewal medicals it is
equally possible to conceal stuff from an FAA or a CAA AME. If somebody has the balls to conceal a heart attack from his AMEs and his GP (which is possible) then all bets are off.
But encouraging the widespread belief that FAA medicals are easy doesn't do anybody any favours. It creates a lot of anti-US sentiment inside the usual places, who are all rubbing their hands at the moment anyway.
FAA medicals are just a lot cheaper...