A third fastball has entered into the fray and Hart is reaping the benefits.
"A few weeks ago, I started throwing a cutter," said the 24-year-old, who is 2-1 with a 3.03 ERA in five games, including four starts, with Triple-A Iowa. "I think I've had a lot of success with that and it's given me another option."
"It's a lot different," Hart said of the difference between his cut-fastball and his sinking two-seamer. "Basically, it's a really hard slider. My fastball is probably 89 to 93 during the game, whereas my cutter will be 84 to 88."
After getting off to a shaky start with a plus-six ERA with Double-A Tennessee following the first two months of the season, Hart has been on fire over the last several weeks.
Prior to being promoted to Iowa, he posted five wins in his last seven starts with Tennessee, hoisting a 2.20 ERA in that span. Entering play this week, Hart leads the Cubs' farm system with 115 strikeouts in 129 2/3 innings. He has fanned 26 in 32-plus innings since being promoted to Iowa.
Now that he's at Triple-A, Hart's success has only continued and there has been little to no painful transitioning period as a result of the call-up.
Hart made his Triple-A debut on Friday, July 13, and allowed five runs (four earned) in six innings. He surrendered three home runs.
Since then, Hart has settled in and yielded three runs or less over his last four outings, giving Iowa eight strong innings on two occasions.
"He's been very aggressive, pitches off his fastball and believes in his fastball," Iowa manager Buddy Bailey said of Hart. "You look at what he's done at Double-A and now here, and it was a great trade by Jim (Hendry)."
Bailey uses Hart and his on-again, off-again teammate, Sean Gallagher, as good examples for other pitchers on his staff to model after.
"They've got a lot of great intangibles for young pitchers and they're blessed with good arms," Bailey said of Hart and Gallagher. "They're bulldogs. They've got the right attitude. When they take the hill, they feel like they're supposed to win. They believe in their stuff and they're aggressive."
Hart has shown the ability to pitch effectively at the upper levels of minor league ball in the months following the trade that brought him to the Cubs.
But what many don't know about the Maryland alumnus and former first baseman is that he also has the ability to help himself with the bat.
Throughout his college career at Maryland and Navarro College in Texas, the right-handed hitting Hart was a force to be reckoned with at the plate.
He batted .369 with eight home runs, 11 doubles and 33 RBIs in his lone season in the ACC in 2004, and had previously earned such awards as the 2003 Rawlings NJCAA Big Stick Award with a .448 average, 11 home runs and 42 RBIs while playing in the Texas Eastern Athletic Conference.
Since Hart was a member of the Orioles' system and was thus exposed to strictly DH leagues throughout the early part of his minor league career, the Plano, Texas, native didn't get much experience in the batter's box at the professional level until joining the Cubs.
Hart now has seven hits in 11 at-bats with Iowa to date, and on three occasions Bailey has called on him to pinch-hit in between starts.
"People know about (Carlos) Zambrano at the big league level, but this guy can stroke it," Bailey said. "He helps himself in every game where we've had National League rules. When he's had a chance to hit, he's helped himself."
Hart has shown great strides this season, particularly with the development of his cut-fastball, but also with the success of his secondary pitches.
"My changeup is coming along nicely," Hart boasts. "It's the first year I've really felt comfortable throwing (it) to hitters to get outs with. To me, my slider is still my out-pitch. It's what I've gotten a lot of my strikeouts with this year and I feel comfortable throwing it in any count."
After Hart first got word that he was going up to Iowa back in mid-July, he admitted the promotion came as quite a surprise.
Tennessee's most consistent pitcher this season has been right-hander Mark Holliman, who has nine wins and a 3.05 ERA in 21 starts, plus a seven-inning no-hitter back on June 21 against Huntsville.
"I knew I was putting seven or eight good starts together in a row and I felt I was coming around, but it was a big surprise to me because we had some other guys at Tennessee that (were) doing that all season," said Hart, who nevertheless saw the promotion as a meaningful gesture by his parent club.
"It feels like the Cubs definitely believe in me and see some ability in me, which is really nice. I like to think that if I keep doing well, I'll get my shot in Chicago," Hart added.
But Hart wants more than just a "shot" with the big league team.
"It's nice to advance a couple of levels during the season and it's always your goal to try to get to the big leagues," Hart said. "At the same time, my goal is not just to get there, but to stay there and have a lot of success."
He may very well be on the right path to do so.