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.
Medalists
edit| Gold | Mitch Potter United States
|
| Silver | Yeimer López Cuba
|
| Bronze | Alleyne Francique Grenada
|
Records
edit| World Record | Michael Johnson (USA) |
43.18 | August 26, 1999 |  Seville, Spain
|
| Pan Am Record | Ronnie Ray (USA) |
44.45 | October 18, 1975 |  Mexico City, Mexico
|
Results
edit| Rank | Athlete | Heats | Final | |
|---|---|---|---|---|
| Time | Rank | Time | ||
| 1 |  Mitch Potter (USA) |
45.62 | 2 | 45.11 |
| 2 |  Yeimer López (CUB) |
45.69 | 3 | 45.13 |
| 3 |  Alleyne Francique (GRN) |
45.31 | 1 | 45.51 |
| 4 | Adam Steele (USA) |
45.83 | 6 | 45.72 |
| 5 |  Shane Niemi (CAN) |
45.89 | 7 | 45.78 |
| 6 |  Carlos Yohelín Santa (DOM) |
45.82 | 5 | 45.85 |
| 7 |  Michael Campbell (JAM) |
45.79 | 4 | 46.10 |
| 8 | Davian Clarke (JAM) |
45.93 | 8 | 46.17 |
| 9 | Glauder Garzón (CUB) |
45.99 | 9 | |
| 10 |  Chris Lloyd (DMA) |
46.53 | 10 | |
| 11 |  Dennis Darling (BAH) |
46.59 | 11 | |
| 12 |  Damion Barry (TRI) |
46.79 | 12 | |
| 13 |  Mauricio Mery (CHI) |
46.92 | 13 | |
| 14 |  Geronimo Goeloe (AHO) |
47.61 | 14 | |
| 15 |  Jonnie Lowe (HON) |
47.78 | 15 [1] | |
| 16 |  Kenneth Telemaque (ISV) |
48.85 | 16 | |
| 17 |  Cristian Gutiérrez (ECU) |
49.88 | 17 | |