| Final | time | L | | | 1. Sheena Johnson |  USA | 54.64s | 4 | | | 2. Nickiesha Wilson |  JAM | 54.94s | 5 | PB | | 3. Nicole Leach | USA | 54.97s | 6 | | | 4. Shevon Stoddart | JAM | 55.42s | 3 | SB | | 5. Andrea Blackett |  BAR | 56.02s | 7 | | | 6. Lucimar Teodoro |  BRA | 56.58s | 2 | | | 7. Janeil Bellille |  TRI | 57.42s | 8 | | | 8. Daimí Pernía |  CUB | 59.71s | 1 | |
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| World Record: | | Yuliya Pechonkina (RUS) 52.34s | | Tula (RUS) 08.08.2003 | | Panamerican Record: | | Daimi Pernia (CUB) 53.44s | | | Winnipeg (CAN) 28.07.1999 |
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| Heats - First 3 and Best 2 progress. |
| Heat 1 | Team | time | L | | 2. Nicole Leach | USA | 55.77s | | | 4. Nickiesha Wilson | JAM | 56.44s | | | 6. Lucimar Teodoro | BRA | 56.99s | | | 7. Daimí Pernía | CUB | 57.45s | | | 10.Daisy Ugarte | BOL | 1:00.26 | | | 11.Lucy Jaramillo | ECU | 1:00.30 | |
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| Heat 2 | Team | time | L | | 1. Sheena Johnson | USA | 55.55s | | | 3. Shevon Stoddart | JAM | 56.40s | | | 5. Andrea Blackett | BAR | 56.54s | | | 8. Janeil Bellille | TRI | 57.71s | | | 9. Higlecia Oliveira | BRA | 58.53s | | | 12.Paola Sánchez | ECU | 1:01.59 | |
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