The New Jersey native posted a photo of himself at the hospital early Monday morning.
The "Clerks" filmmaker says he was in between his comedy shows Sunday night in Glendale, California when he started feeling sick.
"The Doctor who saved my life told me I had 100% blockage of my LAD artery (aka "the Widow-Maker")," Smith said.
If he had not gone to the hospital, his doctor says he would have died.
"But for now, I'm still above ground!" he said.
Smith's show "Kevin Smith Live!" was at the Alex Theater in Glendale, California.
In addition to "Clerks," Smith wrote and directed "Chasing Amy" and "Mallrats," and owns a comic book store featured in the reality television show "Comic Book Men."