Smith, 47, shared the news on Twitter from is hospital bed in California.
"After the first show this evening, I had a massive heart attack. The Doctor who saved my life told me I had 100 per cent blockage of my LAD artery (aka 'the Widow-Maker').
"If I hadn't cancelled show 2 to go to the hospital, I would've died tonight. But for now, I'm still above ground!" he tweeted.
Smith said he cancelled a stand up gig in Glendale, California, after falling ill.