Numminen will practice with the Sabres on Thursday after completing a two-day evaluation, the team announced during the first intermission of their game against Tampa Bay on Wednesday night.
He hasn't been cleared to play in a game. Buffalo has eight regular-season games remaining.
"We'll have a better sense of where his fitness level is and we'll go from there," Sabres general manager Darcy Regier said.
For Numminen, it will be his first time back since he practiced with the team in early January. However, he was informed by team doctors at that time that he wouldn't be cleared to play until mid-March, at the earliest, to allow his sternum additional time to heal.
Numminen had surgery in September to repair a faulty valve, which was discovered during a routine checkup ahead of his 19th NHL season and third with Buffalo.
His return can't come at a better time for an injury-depleted Sabres team that has three regular defenseman -- Jaroslav Spacek (ribs), Dmitri Kalinin (right shoulder) and Nathan Paetsch (concussion) -- out of the lineup.
Numminen re-signed with the Sabres to a one-year, $2.6 million contract in July. He's spent the season on the team's suspended list, so his contract doesn't count against the salary cap. Regier said he'll lift the suspension when Numminen is able to play, and at that time Numminen will begin to get paid.
Numminen has had a heart murmur since childhood. He was diagnosed with a dilated aorta in March 2004, when he was playing for the Dallas Stars, and missed five games before he was cleared to play.
The condition also forced him to miss one game and part of another during a playoff series against Philadelphia in 2006.