Heat opens with a vision of a woman named Mrs. Cora who walks toward the train stop across the street from Yankee Stadium. Baseball and the train are “the two constants” (1) in her life. As she reflects on the importance of baseball in her life, a boy hits Mrs. Cora from behind and steals her purse, which carries the 100 dollars she will use to buy food. Mrs. Cora yells at the boy to stop. As neighbors help her up, they call for the police. Mrs. Cora sees a policeman chase after the thief, whose name, she later discovers, is Ramon.

Ramon, a Dominican teenager from the South Bronx, is “not the smartest sixteen-year old” around, but he is also "not the laziest" (2). Confident in his speed and too disinterested to want to work, Ramon tends to steal to make pocket money. The day that he steals Mrs. Cora’s purse, the police officer chasing him is fat; Ramon wants “to laugh his head off” (3) watching the man try to catch up to him.

But as Ramon passes through Macombs Dam Park on his way home, something hits his head and knocks him down. When he wakes up, he discovers the policeman and another boy, “a tall skinny boy” (4) with a baseball glove on, whose name is Michael Arroyo. The policeman tells Michael “you’ve got some arm, kid” (5).

Chapter 2, told from Michael’s perspective, reflects on his father, called Papi, who “was the first to tell [him] he had the arm” (6). Papi was known in Cuba, the island from which they fled the year before, as Victor Arroyo. There he was a famous Cuban shortstop, and he encourages Michael in his love for baseball. Michael plays along with “his father’s dream” (7) that he make it to the Little League World Series and beyond. “In a few weeks” (8) he is slated to play in the series, but Michael is nervous that he will not make it.

Michael's brother, Carlos, works two jobs to keep the family afloat, and “[explodes]” (10) when Michael mentions their money woes, as their household is financially unstable. Despite this instability, it turns out that Mrs. Cora’s new purse, which Michael helped to return, was a birthday gift from Carlos; they live in the same building.

The Yankees are a preoccupation for Michael and Carlos the same way they are for Mrs. Cora. Down the street from their apartment, “not even hundred yards away” (12), Michael can see the stadium. He stands on the fire escape, listening to announcers on the radio, and imitates El Grande Gonzalez, a hot pitcher for the team. On the fire escape, he “[isn’t] mad at anyone or worried what might happen to him and his brother” (13).

Michael is often alone because their father is absent, although the narrator does not explain why. On the day that Michael returns Mrs. Cora’s purse, Michael’s All-Star team leaves a message on the apartment’s answering machine, asking Michael’s father to drive the team down to the World Series in Pennsylvania. The coach, Mr. Minaya, does not know that their father is gone, but Michael suspects that he knows their father is absent and wonders “if even baseball [is] safe” (14). 

Chapter 3 begins with a description of the baseball fields at Macombs Dam Park, where Michael’s All-Star team, the Clippers, plays. On days without games, “Michael and his friends usually had the Macombs Dam Park field to themselves” (15) for a pickup game. This informal game is the baseball Michael most enjoys. Some days, he and his friends join older boys on the regulation-size field. Michael follows his brother’s and Mr. Minaya’s orders not to pitch from the faraway mound on this field.

The day after he returns Mrs. Cora’s purse, he returns to the field and is greeted by his catcher, Manny Cabrera, the only player from his regular-season team to make the Clippers, and two other Clippers, Kelvin and Anthony. The boys mess around with Michael, acknowledging that they know he was throwing from the mound on the regulation field when he hit Ramon.

As Kelvin prepares to hit, he asks Michael not to throw too hard or to “[try] for the magic number” (19) that day. The magic number is 80: 80 miles per hour, 3 over what Danny Almonte pitched in the Little League World Series before. Manny claims that “hitting 80 at their age was really the same as someone older hitting 110” (19). But Michael knows that he hits 80 sometimes, in practices and in games. He throws much more often than regulations allow him to, outside of games, with his friends. One of Michael’s pitches is so fast that it knocks Manny over. Manny is sure that the pitch traveled 80 miles per hour.

When some older boys show up with enough players for a game, Michael moves to center field, a position he loves, because he “[loves] to move” (24). In the outfield, he daydreams about Yankee stadium, picturing his hero, El Grande, preparing to play. But soon, he notices a “beautiful girl watching them from the basketball courts” (24).

Even though Michael at age 12 rarely notices girls, he does notice this girl’s beauty, and that she “[has] a baseball glove under her arm” (25). She continues to watch until Michael moves to pitch in the fifth inning, against a tall boy who is “a banger” (25). He throws so hard that he makes the older boy swing and miss, but when he looks back at the girl, he is “sure she [is] laughing at him” (25).

After the inning, Michael walks toward the courts and asks her “what was so funny” (26). But the girl turns and Michael marvels at her eyes, her long legs, and how fast she can run “for a girl, for anybody,” as she escapes “up the hill toward Yankee Stadium” (26).