The 54-year-old was hospitalized after experiencing chest pains during Sunday's 7-0 win over the Atlanta Braves in the nation's capital. He missed the team's three-game series in St. Louis after undergoing a cardiac catheterization and remaining in the hospital until Tuesday.
"He had more energy today," Nationals general manager Mike Rizzo said of Martinez on Tuesday, per MLB.com's Jamal Collier. "He's upbeat, like he always is. We talked a little health and a lot of baseball, so it was kind of normal."
In his second season as skipper, Martinez has guided the Nationals to an 83-68 record. They currently own a two-game edge in the National League wild-card race, holding a one-game lead over the Milwaukee Brewers for the top wild-card spot.
Martinez has a career record of 165-148.
Washington has 11 games remaining in the regular season. The Nationals will play three games in Miami before returning home for an eight-game homestand to end the season, which features five games against the Philadelphia Phillies and three versus the Cleveland Indians.