Medina Spirit, the race horse whose victory in the 2021 Kentucky Derby had been called into question by a failed post-race drug test, may have died of a heart attack but a necropsy report was inconclusive, according to California regulators on Friday. Hair, blood and urine samples showed no evidence of doping.

The colt died on Dec. 6 after working five furlongs at the Santa Anita Park racetrack in Southern California. The necropsy was conducted by veterinarians and forensic experts at the University of California, Davis.

“A definitive cause of death was not established despite extensive testing,” the California Horse Racing Board said in a statement.

Medina Spirit had swollen lungs, foam in his windpipe and an enlarged spleen, all common when horses die suddenly, the board said. Those conditions are “compatible with, but not specific for a cardiac cause of death,” it said.

Last year, 13 percent of the 71 racing deaths of thoroughbreds and American quarter horses in California were classified as sudden deaths.

California officials said it is not unusual to reach an inconclusive necropsy result. They cited an international study of exercise-related sudden death in racehorses that found a cause of death was determined with certainty in about 53 percent of cases, a presumptive cause was established in 25 percent, and in about 22 percent the specific cause of death could not be determined.

Neither Bob Baffert, Medina Spirit’s trainer, nor his lawyers, were available for immediate comment.

The necropsy does not resolve whether Medina Spirit’s Derby victory will be allowed to stand. Kentucky racing officials are meeting Monday to determine whether his first-place finish should be vacated. The post-race drug test of Medina Spirit found the drug betamethasone, a corticosteroid injected into joints to reduce pain and swelling. Baffert’s lawyers have said that Medina Spirit had a rash on his hind end, and that an ointment used daily to treat the dermatitis contained the substance.

At stake for the owner, Amr Zedan, is the Derby’s $1.8 million first-place check, which would be awarded to the owners of Mandaloun, the second-place finisher, if Medina Spirit’s victory is invalidated. The victory was also a record seventh in the Derby for Baffert.

The trainer’s reputation and broader future in the sport are in the balance as Baffert has been barred for two years from Churchill Downs, the track that hosts the Derby. New York racing officials have sought to bar Baffert from Aqueduct, Belmont and Saratoga, alleging in a recent hearing that the trainer had committed conduct detrimental to the best interests of racing, to the health and safety of horses and jockeys, and to its business operations.

Baffert is fighting these legal battles at a time when the Triple Crown season is heating up and the quest for qualifying points to earn a spot in the Derby’s starting gate is getting urgent. He has three of the most accomplished 3-year-old colts in his barn — two of them, Corniche and Newgrange, are undefeated.

As it stands, none of his contenders will make the Derby starting gate. Churchill Downs, which hosts the Derby, has refused to award qualifying points to horses Baffert trains.

Last month, Baffert threatened to sue Churchill Downs if the track in Louisville, Ky., does not lift the two-year ban, saying his right to due process was violated and that he had been unlawfully excluded from Churchill Downs and the Derby, according to a wide-ranging draft legal complaint obtained by The New York Times. The complaint has not been filed.

Bill Carstanjen, the chief executive of Churchill Downs, said the suit was “meritless,” threatened to countersue if it were to be filed and emphasized that Baffert was a repeat offender. In the 2020 Kentucky Oaks, the nation’s premier race for 3-year-old fillies, the Baffert-trained filly Gamine tested positive for the same substance as Medina Spirit after finishing third.

In all, Baffert’s horses have failed 30 drug tests over four decades, including five in a recent 13-month period.

At 12-to-1 odds, Medina Spirit was a surprising winner of the Derby, America’s most famous race, in May. The colt was sold as a yearling for only $1,000 and was a bargain for Zedan, who paid just $35,000 for him.

The colt’s legacy is as complicated as it is tragic.

Last November, Medina Spirit finished second to Knicks Go in the $6 million Breeders’ Cup Classic in what was the final race of a career in which the colt won five of his 10 starts for earnings of more than $3.5 million.

It may take years of litigation to determine whether Medina Spirit will remain a Derby winner.