Miller first hurt the shoulder in the third quarter in a collision with the Heat's Mario Chalmers. He immediately clutched his shoulder and was taken to the locker room.
"It felt like it came out of place, went numb," Miller said. "That scared me more than anything."
Miller returned to the bench a few minutes later with his shoulder taped and re-entered the game with about four minutes left in the quarter.
"I thought he played pretty good with one arm," Washington coach Flip Saunders said.
Miller, who was acquired by Washington in a trade with Minnesota in June, aggravated the injury with 9:11 left in the fourth quarter when he fell to the court on a foul by Miami's Joel Anthony. Miller completed the 3-point play and stayed in the game for about another minute before again leaving for the locker room.
The Wizards have already been hit by injuries. Guard Javaris Crittenton had surgery on his left foot on Oct. 23 and is expected to miss another month with a strained tendon in the foot. Forward Antawn Jamison has not played this season after injuring his right shoulder in the preseason.
"Hopefully I'll be a quick healer and see what happens," Miller said.