LEXINGTON, Ky. - El Prado, the son of Sadler's Wells who launched Frank Stronach's Adena Springs stallion operation, has died at age 20. \nThe horse died of a heart attack shortly after being turned out in his paddock Monday morning at about 10 a.m., according to Dermot Carty of Adena Springs in Kentucky.\n"He put us on the map," Carty said. "There's no ifs, ands, or buts about that. He moved his mares up right off the bat. It was a privilege to have him."\nEl Prado's fertility had declined somewhat as he aged, but he still commanded a $75,000 fee in 2009, and he covered a good book of mares for an older horse, Carty said.\n"He could handle a good book of mares, but you wouldn't want to overbreed him," he said.\nAn Irish juvenile champion, El Prado later became America's leading sire in 2002 and was often among the top stallions here. His most accomplished sons and daughters include 2004 champion turf horse Kitten's Joy, Grade 1 winner and hot young sire Medaglia d'Oro, 2005 Breeders' Cup Mile winner Artie Schiller, dual Grade 1 winner Borrego, and numerous other graded performers.\nCarty recalled that Stronach bought El Prado privately from Coolmore Stud in the early 1990s, and when Stronach opened his Adena Springs stallion operation, El Prado was one of the first sires there.\n"We started off dealing seasons at $1,500," Carty said, noting that El Prado's sire, Sadler's Wells, had the reputation as a grass sire - something many commercial breeders in America didn't care for at first. Sadler's Wells turned out to be a great sire and a sire of sires, and El Prado's reputation also grew as he got winners on both sides of the Atlantic. It didn't hurt, Carty said, that he was a son of Drone's three-quarter-sister Lady Capulet, representing one of Claiborne Farm's most memorable families. Lady Capulet, by Sir Ivor, won the 1977 Irish 1000 Guineas in her first start, then placed in two other group events before retiring at age 3.\n"He's given a lot of stamina and put the classic distance back in the breed," Carty said of El Prado, adding that Sadler's Wells on the top line over Lady Capulet's strong American family on the bottom ultimately made El Prado a good fit for American racing.\nCarty said El Prado didn't fulfill his promise at 3 partly because of his attitude.\n"He was a little hot-headed," he explained, "a lot like his mother."\nIrish training great Vincent O'Brien and the late Coolmore co-founder Robert Sangster bred El Prado. Coolmore, Sangster's sons Adam and Ben, and O'Brien, who died this year, retained interests in El Prado when he went to stud for Stronach.\n"It encouraged Frank Stronach to continue to stand more stallions and to build the farms," Carty said.\nCarty said Stronach would likely stand the El Prado winner Singing Saint, now 5, at his Paris, Ky., farm in 2010. \n"How many farms go through their whole run and never get the opportunity to stand a great stallion?" Carty said. "El Prado is not only a great sire, but his racehorses can run short or long, and they can run anywhere. He's had Group 1 winners all over the world.\n"And to become a sire of sires is something very few stallions get to do, and he's on the road to doing it. His daughters will be the next good thing."