At the 2000 Summer Olympics in Sydney, Australia, Sandeno won the bronze medal in the 800 m freestyle event, along with 4th place in the 400 meter Individual Medley and 6th place in the 200 m butterfly. In 2003, while enrolled at the University of Southern California, she won the US national championship in the 200m butterfly, 200 m IM, and 400 m IM events.
The 2004 Summer Olympics in Athens, Greece saw Sandeno win three more Olympic medals: a silver medal in the 400 m IM, a bronze medal in the 400 m freestyle, and a gold medal in the 4x200 m freestyle relay. The American team of Natalie Coughlin, Carly Piper, Dana Vollmer, and Sandeno also broke the seventeen-year-old world record (previously held by East Germany) by more than two seconds with their victory in the 4x200 m freestyle relay.
After failing to qualify for the 2008 U.S. Olympic Team, Sandeno announced her retirement. She is currently looking to start a new career in sports broadcasting. As of May 2010, Sandeno has joined with Think Physical Therapy and started a venture called Swim Tank where she will do stroke analysis for swimmers. For the 2010 Southern California Swim Season, Sandeno was an assistant swim coach at Mater Dei High School, a private catholic high school in Santa Ana, California. As a high school student, Sadeno attended a public high school in Lake Forest.
At a younger age, Sandeno swam for the Nellie Gail Saddleback Valley Gators in Orange County, California, coached by Vic and Renee Riggs. She swam as one of the top competitors in freestyle events, and helped the Gator team.
Sandeno attended El Toro High School in Lake Forest, California and was on the El Toro High School Swim Team.
In September, 2008, Sandeno teamed up withAnna Kournikova and Katya Myers to win the female celebrity category of the 2008 Malibu Triathlon.
In, June 2011 she competed in the 19th Annual Flowers Sea Swim in the Cayman Islands.