Some amazing background from the usual place: A necropsy revealed his heart was significantly larger than that of an ordinary horse. An extremely large heart is a trait that occasionally occurs in Thoroughbreds, linked to a genetic condition passed down via the dam line, known as the “x-factor”. The x-factor can be traced to the historic racehorse Eclipse, which was necropsied after his death in 1789. Because Eclipse's heart appeared to be much larger than other horses, it was weighed, and found to be 14 pounds (6.4 kg), almost twice the normal weight. Eclipse is believed to have passed the trait on via his daughters, and pedigree research verified that Secretariat traces in his dam line to a daughter of Eclipse. In the 20th century, the heart of Phar Lap was weighed and also documented to be 6.35 kilograms (14.0 lb), or essentially the same size as that of Eclipse. At the time of Secretariat's death, the veterinarian who performed the necropsy, Dr. Thomas Swerczek, head pathologist at the University of Kentucky, did not weigh Secretariat's heart, but stated, “We just stood there in stunned silence. We couldn't believe it. The heart was perfect. There were no problems with it. It was just this huge engine.”In the fall of 1989, Secretariat was afflicted with laminitis—a painful and often incurable hoof condition. When his condition failed to improve after a month of treatment, he was euthanized on October 4 at the age of 19. Secretariat was buried at Claiborne Farm in Paris, Kentucky, given the rare honor of being buried whole (usually only the head, heart, and hooves of a winning race horse are buried, and the rest of the body is cremated).