"It's still very hard for me to process all of this," Lundqvist said in a video posted on social media by the Capitals. "And kind of shocking, to be honest."
Calling it "a pretty tough and emotional day," the longtime New York Rangers goaltender, who joined the Capitals this offseason, said he has been undergoing various tests on his heart "for several weeks."
"After lots of discussions with doctors around the country, and finally receiving the last results earlier this week, I unfortunately won't be able to join the team this year," Lundqvist said.
A message from Henrik: pic.twitter.com/JJDe2lKAXz— Washington Capitals (@Capitals) December 17, 2020
Lundqvist, 38, thanked the Capitals in another post on Twitter, saying, "I will take the next few weeks to be with my family and I'll be back to share the next steps."
This offseason, Lundqvist agreed to a one-year deal with the Capitals worth $1.5 million after a 15-year run with the Rangers. He became an unrestricted free agent in a crowded field of goaltenders.
"Heartbreaking and emotional," Capitals owner Ted Leonsis wrote on Twitter. "I am only concerned and thinking about Henrik Lundqvist as a person and for his family's wellbeing. We pray for his good health. We and the entire NHL family support the King."
NHL commissioner Gary Bettman called Lundqvist "a beloved player" and a "wonderful ambassador" for the sport.
"While we are all saddened as hockey fans that we will not be able to watch Henrik tend goal for the Capitals this season," Bettman said, "we are also thankful that he will be getting the necessary medical care."
The Rangers also offered their support on social media.
"We have no doubt that Henrik Lundqvist will face this challenge with the same fierce determination and grace that made him one of the greatest goaltenders to ever play the game of hockey, and an inspiration to all of us," the team's statement said. "He and his family are in our thoughts during this difficult time. He will always be a part of the New York Rangers family."
Lundqvist is a five-time finalist for the Vezina Trophy, winning the award for the NHL's top goaltender in 2011-12.
He has appeared in 887 NHL regular-season games, plus 130 in the playoffs, and he came close to a championship in 2014, leading the Rangers to the Cup Final. He lost postseason series to the Capitals in 2009 and 2011, then eliminated them in 2012, 2013 and 2015.
He hadn't participated in the playoffs with New York since 2017 until two games in the qualifying round of the expanded, 24-team playoffs this past summer.
"The risk of playing without remedying my condition is too high," Lundqvist wrote on Twitter, "so I will spend the coming months figuring out the best course of action."
ESPN's Emily Kaplan and The Associated Press contributed to this report.