A general principle of pitching effectiveness is that separation of speeds is more important than the speeds themselves. Everything else being equal, a pitcher who can consistently throw his fastball at 88 mph and a secondary pitch at 68 has an enormous advantage over a pitcher who throws his fastball at 98 and his secondary pitch at 92.

Many of the game’s best pitchers take this a step further. Eric Gagne throws a fastball in the high 90s, a change in the high 80s, and a breaking ball in the high 70s, all with a similar delivery. Pedro Martinez, Orlando Hernandez, and John Smoltz all throw at least three pitches with large differences in velocity. Roger Clemens and Randy Johnson, each of whom won multiple Cy Youngs throwing 95+ mph fastballs and high-80s breaking balls, have each mixed in an off-speed pitch (a curve and a change, respectively) in recent years, helping them dominate as they’ve aged.

The Mets’ Aaron Heilman doesn’t yet fit in with this select company, but he has emerged as one of the most intriguing stories in Flushing this year, largely because he’s learned the importance of changing speeds. Heilman was a terrible pitcher in 2003 and 2004 – over those two years, his ERA was 6.36 over 18 starts – for many reasons. He’d changed the delivery that had made him a first-round pick, causing his pitches to flatten out and costing him command. He was tentative and hesitant with his pitches when he should have been aggressive, and aggressive when he should have been cautious.

Worst of all, Heilman was essentially throwing batting practice. His fastball came in the upper 80s, and his change in the lower 80s, neither with much movement. A hitter could gear up for the fastball, and if he got the change, adjust to it without much effort. You never saw many swings and misses against Heilman, and his strikeout rates were low; this was because he wasn’t fooling anyone.

This season, Heilman has shown signs of becoming a major league pitcher. He was awful in his first and third starts of the season, but the complete game 1-hitter he threw against Florida on April 15 was, it seems, not an isolated event but the sign of Heilman putting things together. He also enjoyed quality starts against Atlanta and Washington, both good hitting teams, and a strong relief appearance against the Phillies. On Monday night, despite missing an hour and a half to rain delays, Heilman threw well against the Cubs, pitching 5 1/3 innings and giving up two runs. His record stands at 3-2 with a respectable 4.08 ERA. What’s he doing differently?

Everything, pretty much. Heilman has changed his delivery so that he’s now whipping his arm across his body, which isn’t ideal but seems to have added some movement to his pitches. He’s been consistently throwing strikes and reaping all the benefits that come with that, such as working ahead in the count and getting easy outs on groundballs. And he’s separating the speeds on his pitches.

On Monday night, staked to a three-run lead before he took the mound, Heilman started off the hitters with two-seam fastballs for strikes, mixed in his changeup and then went with the four-seam fastball, a wise approach against an impatient Cubs lineup. The main difference in the two fastballs is their action; both were a bit flat, but the two-seater moved down as it crossed the plate while the four-seamer rose and had a bit of a jump, which is in theory what is supposed to happen. The two-seamer came in at 88 or 89, the four-seamer at 90 or 91, while the change varied from 78 to 81.

None of this sounds much different than what he was doing when he was getting knocked around like a pitching machine, but it really is. Last year, Heilman was typically throwing from about 80 to about 88; a range of 78 to 91 is half again as big. That difference is significant – Heilman is changing hitters’ bat speeds enough to induce weak swings at changeups and loping swings at moving fastballs.

Why hasn’t Heilman simply done this before? It’s quite a lot easier for me to sit here and write about it than it is for an athlete to do it. Small variations in a pitcher’s delivery that make pitches move more and small variations in speed are matters of touch and feel and they have to do with confidence, injury, and a dozen other factors.

The important thing is that Heilman has shown he has the ability to get ahead of hitters, change speeds, and locate his pitches. Those may be things that announcers, managers, and coaches harp on so much that they just seem like jock-speak, but they are really the keys to big-league success.

Maybe even more than any of that, though, Heilman is exhibiting newfound determination and professionalism. Monday, on a damp night when he’d been held out for an hour, Heilman warmed up, took the ball, and pitched well when he had a real reason not to. Last month, after getting whacked for seven runs in four innings against a Marlins team he’d dominated days before, Heilman came back and allowed one run in seven against the Braves. Anyone who saw Heilman in 2003 saw a pitcher who didn’t look like he wanted to be in the majors. He’s not that pitcher anymore.