My dad suffered his first heart attack when I was a kid. We didn't know exactly what was happening with him, as he suffered it while out of town. I remember him coming home & being how you described- moody, short tempered, etc. We all kind of walked on egg shells around him.
Your husband may be depressed. My mom talked to the Dr. about how Dad was acting & Dr. put him on Zoloft. He was a very changed man

Of course, this was 20 years after his first heart attack. My childhood would've been totally different had he been on it then
He may also feel that life is short so he wants to make sure he lives to the fullest (opinionated, critical, etc.). It's possible that this "new person" has been inside your husband all along & now he's decided to not supress that personality anymore because of his close call with death.