Why do some pains come surrounded by top?

Some pains seem to come contained by waves. Like during a heart attack, i've hear it "strikes" per second or so. I know it's doesn't go next to heartbeat, so what is it then and why? Is it in recent times random, or is at hand a pattern within which pain strikes?Why do some pains come surrounded by top?
Maybe the adrenaline is trying to purloin the pain away but it is worn-out for whatever source.
Or it could be cramping muscles.
well it have to do with the blood stream
depends on the character cuz pain is subjective.