Lundqvist announced Monday on Twitter that he will undergo an "aortic valve replacement, aortic root and ascending aortic replacement."
The 38-year-old Lundqvist said: "Last 3 weeks my focus has shifted from training camp and the upcoming season to my health and what I can and can't do."
Lundqvist, who signed a one-year deal to join the Capitals after spending 15 seasons with the New York Rangers, announced earlier this month that he would miss the entire upcoming season because of the heart issue.
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 Stanley 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.