Kalas was found unconscious in the team's broadcast booth around 12:30 p.m. ET, and he was taken to George Washington University Medical Center. Team officials quickly cleared the clubhouse to talk to the players, coaches and staff.
The cause of the death is unknown, but Kalas missed the beginning of Spring Training after having an undisclosed medical procedure. He was in good spirits when he arrived in Clearwater, Fla., eager to follow the Phillies for another season.
Todd was not at Tropicana Field for the Rays' home opener against the Yankees on Monday night, but he was on the minds of members of the Rays family.
"For Todd and his family, it's just an awful moment and we send our sympathies, and I can't wait to visit with Todd in person," Rays manager Joe Maddon said.
Maddon hails from Hazleton, Pa., so he understands the magnitude of Kalas' passing.
"He was definitely a part of the culture, not only in Major League Baseball, but sports in general and definitely in that part of the world," Maddon said. "I remember listening to him growing up. And I know that people back there are going to take it very hard."
Rays play-by-play voice Dewayne Staats said Todd called him earlier on Monday to tell him his father had passed and that Todd seemed to be taking it as well as he could.
"Harry was the personification of taking his gift and doing what you're supposed to do with it," Staats said. "He enjoyed it. It's a great gift. And he made sure that he took full advantage of that, and as he transitions from this life into the next one, what better place to do it than at the ballpark, in the booth? And if Harry could have written it his way, that's exactly the way he would have written it."
Staats said he felt like he had known Harry Kalas since 1965, when Kalas called Houston Astros games.
"I was a little kid listening to him broadcast Jimmy Wynn home runs at the Astrodome," Staats said. "And his home run call was, 'And that ball is in Astros orbit.' So I feel like I've known him for a long time. And then in the mid '70s, '76 or '77, I got to know him when I joined the Astros full-time."
Staats remembered Kalas as being quick to help nurture a young broadcaster, such as himself when he first got into the business.
"Harry as a veteran broadcaster was nothing but gracious," Staats said. "He was really kind to a young broadcaster trying to feel his way. And I've always had just great warm feelings for him. So when Todd became part of our crew in the beginning, doing what he's doing, it was like, 'Yeah, that's right, that's what he should be.'"
Longtime baseball man Don Zimmer knew Kalas for many years and said simply, "He was a great man."
"I've known him as long as he's been announcing," Zimmer said. "I always saw him at ballparks, and we always kidded with each other. I saw him at restaurants, just a great guy, classy individual.
"When I walked in here and heard that news today, I couldn't believe it. My god, 73 years old, he's young. He was a great man. Everybody loved him. And I loved listening to him. I heard him call many games. It's a sad story."
Dave Wills, who is part of Tampa Bay's radio broadcast, spoke of seeing Kalas when the Rays played the Phillies in Philadelphia for their final two games of the spring.
"Obviously, he looked a little frail from having some of the issues that he suffered through during the spring," Wills said. "But I don't think anybody thought he wasn't going to be among us in a couple of weeks. It's tough. I feel for Todd and his family. And I feel for the city of Philadelphia. He was their voice. The voice of a generation and one of the great voices of this game and is going to be sorely missed."
Andy Freed, who shares the radio booth with Wills, called the situation weird.
"We're so used to thinking about everything in terms of baseball," Freed said. "But I'm thinking of Todd today as I would my own father. It's just horribly sad. I think of it as a family member would, losing your own dad and not being able to share things with him anymore."
The Phillies, who postponed their scheduled visit on Tuesday to the White House, said funeral arrangements are pending. In addition to Todd, Harry Kalas is survived by his wife, Eileen, and his other two sons, Brad and Kane.