The Men's 400 meter freestyle event at the 2003 Pan American Games took place on August 15, 2003 (Day 15 of the Games).
| 3:40.08 | 2002-07-30 |  Manchester, United Kingdom | |||
| 3:50.38 | 1991-08-16 |  Havana, Cuba |
| Place | Swimmer | Heats | Final | ||
|---|---|---|---|---|---|
| Time | Rank | Time | |||
| 1 | 3:54.12 | 2 | 3:50.01 [1] | ||
| 2 | 3:52.66 | 1 | 3:52.62 | ||
| 3 | 3:58.84 | 5 | 3:54.82 | ||
| 4 | 3:56.69 | 3 | 3:56.64 | ||
| 5 | 3:58.46 | 4 | 3:57.89 | ||
| 6 | 3:59.15 | 6 | 3:58.57 | ||
| 7 | 4:01.79 | 8 | 4:01.86 | ||
| 8 | 3:59.38 | 7 | 4:03.10 | ||
| 9 | 4:02.00 | 9 | 4:01.41 | ||
| 10 | 4:07.87 | 11 | 4:05.03 | ||
| 11 | 4:08.53 | 12 | 4:08.20 | ||
| 12 | 4:14.60 | 15 | 4:09.20 | ||
| 13 | 4:10.75 | 13 | 4:10.16 | ||
| 14 | 4:11.82 | 14 | 4:10.81 | ||
| 15 | 4:15.74 | 16 | 4:15.44 | ||
| 16 | 4:16.14 | 17 | 4:17.18 | ||
| 18 | 4:20.83 | 18 | |||
| - | 4:03.92 | 10 | DNS | ||