[1] Hart attended Jesuit College Preparatory School of Dallas and played collegiately at the University of Maryland before being selected by the Baltimore Orioles in the 11th round (319th pick) in the 2004 Major League Baseball Draft.

Hart's debut came under difficult circumstances, as he was summoned to relieve Will Ohman in the 8th inning of a game against the Los Angeles Dodgers with the bases loaded and nobody out.

After walking the first batter (former Cub Ramón Martínez) on 4 pitches to force in a run, Hart struck out Mark Sweeney, and Rafael Furcal hit into an inning-ending double play.

Despite his inexperience, manager Lou Piniella showed a willingness to use Hart as the Cubs progressed through the stretch run of a pennant race, and he appeared in several close games in September.

[4] Hart was optioned to the Single-A Peoria Chiefs after the game in order to continue to pitch on his regular schedule while the Cubs were on the All-Star break.

Just hours before the trade Hart started for the Cubs against the Houston Astros, he went six innings and gave up three earned runs while recording his third win of the season.