Dunn, who was wearing his baseball uniform, and Uecker have been great friends since Dunn played for the Reds.
"I've known the guy for a long time," Dunn said. "It's good to see him healthy, having fun and back doing what he loves. It was great."
Nationals manager Jim Riggleman appeared not to be happy Sunday afternoon when he learned that Dunn was in the broadcast booth the previous day.
"I wish you wouldn't have told me that," Riggleman said while laughing at the same time.
Riggleman declined to comment after that.
Asked if he would get in trouble for being in the booth during the game, Dunn said: "If I get in trouble going up and seeing a guy after he had heart surgery, I'll pay my fine. That's ridiculous."