Guimond was an MP for almost 20 years, holding the riding of Montmorency-Charlevoix-Haute-Cote-Nord between 1993 and 2011.
"It (the death) has really shaken us," said former Bloc colleague Pierre Paquette, who added that Guimond was in shape and exercised often. "We didn't expect it."
Paquette said Guimond had a lot more to give to the Quebec sovereignty movement.
"He was extremely engaged in everything he did," Paquette said. "He didn't let things go easily, but he was also open to discussion and to getting behind the ideas of others."
Guimond was a lawyer by training who resumed practising after he became one of the many Bloc MPs defeated by the New Democratic Party's so-called "Orange Wave" in the 2011 federal election.
He ran unsuccessfully for the Parti Quebecois in last April's provincial election and became chief of staff last year for Democratie Quebec, a municipal party in Quebec City.
"We have all lost a friend," said Paul Shoiry, head of Democratie Quebec.
The Bloc tweeted Monday that Guimond "gave his life to Quebec. Thanks for everything, Michel."
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