The trade, a dramatic move by first-year Phoenix general manager Steve Kerr, signals an unexpected change in philosophy for the Suns, adding a 7-foot-1, 325-pound center who has won four NBA championships but has been plagued by injuries in recent years and turns 36 next month.
O'Neal has been out with a hip injury and underwent an MRI exam in Miami on Tuesday. He flew to Phoenix on Wednesday for the physical.
"I'm well aware that I'm on the line," Kerr told The Associated Press. "That's my job. That's why I'm sitting in this seat. I'm comfortable with the decision. I think it gives us a better chance to win, and a better chance to win in the playoffs."
The Suns' Amare Stoudemire is a friend of O'Neal and talked to him about his new team.
"He says he's ready to roll," Stoudemire said. "Whatever he needs to do he's going to be down for it, and he wants to win a championship, so we're on the same page."
O'Neal was to be introduced at a news conference Thursday.
He has averaged 25.6 points and 11.5 rebounds in his 14-plus NBA seasons.
This season, plagued by injuries and going through a divorce,he's avera ging 14.2 points. His 14-year streak as an All-Star choice came to an end this year.
He missed much of the 2006-07 season with a knee injury and finished that season with career-lows in games (40), scoring (17.3 points), rebounds (7.4), minutes (28.4) and free-throw percentage (.422).
"It was a very, very hard decision for me. When Shaq came to the team four years ago, I always felt it was forever. We won a championship with him. We wish him nothing but the best," Riley said. "We have to move on with our team. We're rebuilding. This is not the most desirable place to be right now."
He denied that there was any lingering rift with O'Neal.
"I loved Shaq when I got him and I love him today," Riley said. "I've been coaching 25 years and there wasn't anything that went on between Shaq and I that caused this. We simply looked at the big picture, where we are today, and we need to build around Dwyane (Wade)."
The Heat have lost 19 of their last 20 games and have the NBA's worst record at 9-37.
Phoenix gambled that Shaq will be healthy and more motivated when he moves to the desert.
"I do believe we showed Shaq a tremendous amount of respect by sending him to a contender, probably the top contender in the Western Conference and he's going to flourish there, he will help them," Riley said. "He will give them a new life and a new hope and a different game and so I think from that standpoint, he's happy about that."
For the three-plus seasons since Steve Nash came to town, the speedy Suns have been darlings of NBA fans grown weary of the slow style that has prevailed for years. But the Suns have fallen short in the playoffs, never making it to the finals.
The addition of O'Neal doesn't necessarily put the brakes on the running game, Kerr said.
"We ran when Kurt Thomas was here. He got the rebound, and everybody else ran down the court," Kerr said. "We're still going to run, but we feel like we'll have a better halfcourt team."
Marion, weary of being third fiddle to Nash and Amare Stoudemire, asked to be traded before the season began. He didn't get his wish and, although he refused to talk publicly about it, remained unhappy with his role.
Still, his talents fit well with the fast-paced style that coach Mike D'Antoni wanted, especially with his ability to finish on a fast break. He also was the team's best defender, guarding everyone from Tony Parker to Yao Ming. Marion, who has spent all of his 8½ NBA season with Phoenix, made the All-Star team five times, including the last three seasons.
This year, though, he failed to make it, while Nash and Stoudemire did. Marion has NBA career averages of 18.4 points and 10 rebounds. This season he's averaging 15.8 points and 9.9 boards.
The Suns have the best record in the West (34-14) but have not played up to their own expectations. Their interior defense is among the NBA's worst. Kerr apparently felt that without a large presence inside, Phoenix could not combat the big men, such as Andrew Bynum and Tim Duncan, in the playoffs.
With O'Neal on the court, an obviously happy Stoudemire can play his more natural power forward position.
"There's not as much pressure now, as far as being that center position, that center stopper," Stoudemire said. "I've been playing out of position for four years now. Now I'm back at my natural position. Shaq is the best at his and I'm the best at mine, so it's going to be great opportunity for us."
O'Neal's move west adds fuel to the already intense rivalry between the Suns, the Lakers and his old teammate Kobe Bryant.
"Maybe now I won't be the No. 1 enemy when we go there," the Suns' Raja Bell said. "That's OK with me."
The trade required a significant financial commitment from the budget-conscious owner Robert Sarver because O'Neal is scheduled to make $20 million this season and $20 million more each of the next two.
Marion makes $16.4 million this year and could opt out of the $17 million final year of his contract after this season. Banks has been in and out of the Suns' rotation the past two seasons.
The Heat also waived Luke Jackson.
O'Neal entered this season talking about how he wanted to win at least one more title, saying his "legacy" wouldn't be complete unless he left the game with at least five rings.