I think you might be misunderstanding the word "leak" here. 

I sounds like your brother had a heart attack or some other type of serious heart situation. If an artery in the heart gets clogged or "clotted" that part of the heart doesn't get oxygen and it will start to die, this triggers the heart to then start to release a certain type of "enzymes" in the blood. 

When a person goes to the hospital with chest pain, they test the blood, if they see these "enzymes" in the blood it will mean that they probable had a heart attack.  A heart attack is another term for a "clotted artery" in the heart. So it sounds like your brother had a heart attack. 

Normally they will do more tests, like a angiogram to see if he really has clogged arteries, how many, and how bad. Sometimes they install a stent right away really fast to fix a clot, but if its bad he will need open heart bypass surgery. And then sometimes it turns out it was OK and no arteries are clogged. The heart is a crazy and complicated organ.

I'm sorry it took you over a day to get this answer. But I'm sure a Registered Dietitian would have answered you sooner or later.