Doctors at Abbott Northwestern Hospital performed an angioplasty and inserted two stents in his arteries, the (Minneapolis) Star Tribune reported.
Rybak, 58, who left office last week after wrapping up his third term, had a "serious" heart attack, John Stiles, his firmer spokesman said.
The former mayor was expected to be hospitalized for several days.
Rybak was skiing alone in Theodore Wirth Park when he felt shortness of breath and chest pains after covering several miles, then came upon some friends in the park, who called 911.
The Star Tribune said by late afternoon, Rybak was feeling good enough to tweet about his situation in verse: "My cardiac surprise/Gave me quite a start/But it proves this politician/Has a great big heart."
He added, "By the way the ski trails at Wirth are awesome today."
Rybak is now head of Generation Next, a partnership of education, community, government and business leaders seeking to narrow the achievement gap between white and minority students.