I remember it. What a magnificent beast he was. I adored Secretariat. And I like his owner, groom, jockey, and trainer. What a fun time of life that was.
From https://www.derbymuseum.org/Blog/Article/324/Secretariat-s-Heart:
"The average Thoroughbred's heart weighs about 8.5 lbs. Secretariat's heart weighed nearly three times that number! ... Secretariat's big heart likely contributed to his stamina on the racetrack."