Denver also opened as an 8-point home favorite in Game 1 on Thursday, with an over/under of 219.
The Heat are only the second 8-seed to capture a conference championship, and just the third team to win its first three series as an underdog. Miami has racked up a 13-5 postseason record against the spread, winning a record-tying nine games outright as an underdog.
"Miami's playoff run has really solidified the fact that they're a team built for the postseason," David Lieberman, lead NBA oddsmaker for Caesars Sportsbook, told ESPN. "We've seen it a couple of times over the past three seasons, but everyone seemed to forget about that over the course of the regular season. [Jimmy] Butler and [coach Erik] Spoelstra are able to find a new gear come playoff time."
The Heat were 200-1 championship long shots before defeating the Chicago Bulls in an elimination play-in game. Prior to their playoff opener, the Heat had 150-1 odds.
Miami could potentially see the return of 2022 Sixth Man of the Year Tyler Herro, who suffered a broken hand in the team's playoff opener on April 16 and has not played since. Herro said at the time the injury would require four to six weeks of recovery, and that he would hope to be back in time for the NBA Finals should the Heat advance.
"I am unsure an announcement with Herro will change much," DraftKings sportsbook director Johnny Avello told ESPN. "We have to put up the series price now and just go with the current rosters. We will adjust after each win."
Sportsbooks will offer numerous proposition bets for each game and the entire series. Nuggets superstar and two-time league MVP Nikola Jokic is a -125 favorite to average a triple-double in the Finals.