For English native speakers. What does this "it" refer to?

A Heart Attack.

And that short, few-hour exposure is able to trigger a heart attack where they might not have had [A Heart Attack] for days or months, or never.

A heart attack.

"And that short, few-hour exposure is able to trigger a heart attack where they might not have had [heart attack] for days or months, or never."

Hello, the word "it" in the article refers to a heart attack. I clicked the link and read the article. It is a terribly written sentence, but when you read the complete sentence, you can tell the author is referring to a heart attack. Hope this helps... (oh and that article is over a year old... why are you asking a ?? now ha ha)

interior sight English speaker is more suitable advantageous. The order of words is really major in English; to assert "interior sight English speaker" is to assert that he's interior sight to the conversing of English. to assert "English interior sight speaker," is to assert that he's a speaker of "English interior sight," or an English speaker of "interior sight," which makes no experience.

heart attack

he is almost definitely referring to the exposure to the exhaust its really the only way the sentence make Sense

This is a confusing statement for anyone, but I believe it refers to exposure.