| Event: | Men's 400 metres |
| Win Label: | Winning time |
The final of the Men's 400 metres event at the 2003 Pan American Games took place on Friday August 8, 2003, with the heats staged a day earlier in the Juan Pablo Duarte Olympic Stadium in Santo Domingo, Dominican Republic.
| 43.18 | August 26, 1999 | ||||
| 44.45 | October 18, 1975 |  Mexico City, Mexico |
| Rank | Athlete | Heats | Final | |
|---|---|---|---|---|
| Time | Rank | Time | ||
| 1 | 45.62 | 2 | 45.11 | |
| 2 | 45.69 | 3 | 45.13 | |
| 3 | 45.31 | 1 | 45.51 | |
| 4 | 45.83 | 6 | 45.72 | |
| 5 | 45.89 | 7 | 45.78 | |
| 6 | 45.82 | 5 | 45.85 | |
| 7 | 45.79 | 4 | 46.10 | |
| 8 | 45.93 | 8 | 46.17 | |
| 9 | 45.99 | 9 | ||
| 10 | 46.53 | 10 | ||
| 11 | 46.59 | 11 | ||
| 12 | 46.79 | 12 | ||
| 13 | 46.92 | 13 | ||
| 14 | 47.61 | 14 | ||
| 15 | 47.78 | 15 [1] | ||
| 16 | 48.85 | 16 | ||
| 17 | 49.88 | 17 | ||