A deadly mystery at Del Mar, Southern California's premier race track.
10 horses have died in the first 3 weeks of the summer season.
This includes a 3 year-old thoroughbred who collapsed this weekend from a heart-attack in the final seconds of this race.
It's the 3rd heart-related death.
Other horses have been "put down" after injuries.
Many are blaming Del Mar's brand new $6,000,000 grass turf track
Several jockeys have been injured and some nervous owners are pulling their horses off the grass track.
The turf course is now shut down as track officials try soften it with water.
It's unclear whether any of these deaths are connected or simply coincidence.
Racing watchers say they mean a public relations nightmare for the racetrack.