Secretariat was without question the greatest thoroughbred racehorse ever (and at the time he ran I despised that horse). I really want to know what was going on during breeding season 1969 as in 1970 not only Secretariat but Sham and Forego were also foaled.
Secretariat's official time in the Preakness was mistimed and that is the only reason it isn't the record for that race. He and Sham had the fastest two times in both the Derby and Preakness (I believe Sham is now 2 & 3 in the Derby and Preakness respectively) and Sham broke a tooth in the gate and was spitting blood for the entire race.
Secretariat's heart was just shy of 22 pounds. The second largest on record was Sham at ~ 18.5 and going into that triple crown season many felt Sham would go on to become the greatest speed horse of all time (he fractured a hoof in the Belmont and never raced again). While he ended up in anonymity (save a Disney movie that tried to make it appear that a horse could have been favored over Secretariat in the Belmont), I many ways his role was to illustrate Secretariat's greatness as if the two hadn't run the same year, a lingering questioning may well have been "Yes, Secretariat was a better horse but would he have beaten Sham in either of the shorter (Derby, Preakness) races?". As they went head to head the question never needed to be asked.
If anyone has interest look up the record of Forego. He is considered the greatest gelding ever, has many records for victories and finishing in the money. For years (when purses were well below what they have become) he had the highest total career earnings for any racehorse. That three horses of that quality were born in the same year is amazing.