This study was conducted to examine how the number of soccer players and pitch area affect their heart rates during a match. Subjects were male high school students who were members of soccer clubs. They played three matches with varying numbers of players on each of the 75 × 44.5 (three, six, and nine players in one team) and 44.5 × 25 (three, six, and nine players in one team) meter pitches, and played one match on the 90 × 68 meter pitch for seven minutes. We measured the heart rates of players during the last two minutes of matches, and calculated mean values. The results were as follows: 1. In matches played on the small pitch, as the number of players increased, the lower heart rates were observed. As the number of players increased, larger differences in the heart rate were observed among players: 176.3 ± 12.8 bpm in the 3 vs. 3 match (5.4 players/1,000 m2); 159.2 ± 18.8 bpm in the 6 vs. 6 match (10.8 players/1,000 m2); 157.8 ± 17.2 bpm in the 9 vs. 9 match (16.2 players/1,000 m2). 2. Also, in matches played on the large pitch, lower heart rates were observed as the number of players increased. As the number of players increased, larger differences in the heart rate were observed among players: 180.5 ± 11.9 bpm in the 3 vs. 3 match (1.8 players/1,000 m2); 177.3 ± 14.9 bpm in the 6 vs. 6 match (3.6 players/1,000 m2); 162.3 ± 19.2 bpm in the 9 vs. 9 match (5.4 players/1,000 m2). 3. When the number of players per unit area was larger, the heart rates were significantly higher, which demonstrates that the area of the pitch affected the heart rates of players during the match.