A man was stabbed in the heart and remains in critical condition after he accidentally bumped shoulders with another pedestrian while walking and texting in downtown Toronto, police said Wednesday.

The 33-year-old was sending a message on his phone just after midnight when he bumped the passerby, who took the contact as a "perceived slight" and allegedly attacked him, police said.

Constable David Hopkinson said the man's attempt at self-defence only further offended the two suspects, one of whom then allegedly stabbed him in the heart.

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The alleged victim was rushed to hospital, where he was last reported in critical but stable condition.

Hopkinson said the incident near Yonge-Dundas Square seems "totally unique or random."

"It seems like it makes no sense."

A suspect was arrested shortly after while another is sought by police.

Mohamed Ali, 27, is charged with attempted murder and aggravated assault.

Police describe the second suspect as white, 5-foot-8, with short dark hair, and a chin strapped beard. They say he was wearing a black and white sweater and may be familiar to those in the Yonge-Dundas area.