Pietrangelo has been a member of the St. Louis Blues since 2008, and Torey Krug has played for the Boston Bruins since 2011, but there is a chance both could move away during free agency in 2020.
The two defensemen will be the most-coveted players at that position, and they could be lured away with lucrative proposals from teams with large amounts of salary cap space.
Before the 2019-20 campaign, Tyson Barrie fell into the same category as Pietrangelo and Krug. He was traded from the Colorado Avalanche to the Toronto Maple Leafs in July.
If Pietrangelo and Krug remain loyal to their respective franchises, Barrie would be the best defensive option on the market when the season concludes.
Free-Agent Predictions For Top Defensemen
Pietrangelo has been a fixture in the St. Louis defense for over a decade, and he has come into his own offensively over the last four years.
The 30-year-old racked up at least 13 goals and 28 assists in each of the last four seasons, and he boasts a career-high 16 tallies this season.
His increased offensive production combined with his defensive abilities will make him one of the top overall free-agent targets behind Taylor Hall of the Arizona Coyotes.
One of the only arguments against St. Louis giving him a new long-term contract is his age.
If Pietrangelo's abilities decline toward the back end of the potential deal, the Blues could be criticized for spending too much money on him.
But that is a risk the reigning Stanley Cup champion may have to take to keep Pietrangelo away from a long list of potential suitors.
A handful of teams at the bottom of the standings, like the Ottawa Senators and Detroit Red Wings, are in line to have large amounts of salary cap space and could entice Pietrangelo to sign elsewhere.
Spending that much on the top end of the roster has reaped rewards already, and if St. Louis follows that strategy with Pietrangelo, the two sides could stay together for a few more years.
Prediction: St. Louis keeps Pietrangelo.
Krug might be in an even better situation if he opts to remain with the only franchise he has played for.
There should be plenty of intrigue for Krug to stay put since the Bruins sit at the top of the Eastern Conference standings.
Just like Pietrangelo with the Western Conference leader, Krug could struggle to find a better situation to chase after the Stanley Cup on a year-by-year basis.
Krug will earn interest on the market because of his string of 50-point seasons. With one more goal or assist, he will have four straight campaigns with 50 points.
He currently owns nine goals and 40 assists. The scoring tally is his second-highest over the last four seasons.
If the Bruins keep Krug at his current salary or higher, they would have seven players earn over $5 million next season.
With four of the top earners 32 or older, the Bruins may feel some pressure to keep the core intact to make one or two more runs at a title before they have to move on from that group.
Prediction: Krug remains in Boston.
Barrie could be rooting for Pietrangelo and Krug to remain in their respective markets so he could have multiple teams fighting for his signature.
In five of his last six seasons with the Avalanche, Barrie recorded 10 or more goals, and he finished his time there with back-to-back 50-point campaigns.
Unfortunately, he has struggled to put up similar numbers with the Maple Leafs. He has five goals and 34 assists through 70 games.
That dip in production may concern some potential suitors, but his track record in Colorado should serve as a counter to that argument.
It is unlikely he lands back with Colorado since he was traded away after it put trust in a handful of young defensemen.
An intriguing option could be the New Jersey Devils, who made a splash at the position last offseason by acquiring P.K. Subban.
New Jersey will have $30.7 million in salary cap space available, and the addition of Barrie could vault them back into the Eastern Conference playoff hunt.
If Barrie wants to sign with a current contender, the Dallas Stars, Calgary Flames and Minnesota Wild are all expected to have over $20 million in cap space.
Barrie is making $6 million this season, so he could demand a higher deal if Pietrangelo and Krug stay put.
The 28-year-old should have plenty of suitors, but the Devils could be most intriguing because of their cap space and young core that is building toward future success.
Prediction: Barrie lands with New Jersey.
Follow Joe on Twitter, @JTansey90
Statistics obtained from Hockey Reference
Contract information obtained from Spotrac