10-year-old Niceonefrankie pictured here at Cheltenham in 2014
David Davies/PA Archive
No More Hereos died on Wednesday and 10-year-old Niceonefrankie died on Thursday.
Six-year-olds Long Dog and Montdragon died on Friday, the Festival's final day.
Campaigners say 52 horses have died at Cheltenham since 2000. Eight horses died in 2006.
They are now lobbying for change in the horse racing industry.
Dene Stansall, a horse racing consultant with the group Animal Aid, said: "The horses, who are supposedly cherished by the world of racing, are merely disposable commodities, as we have seen this week."
The British Horseracing Authority (BHA) says that fatalities have fallen by a third in 30 years.
It says it will work closely with the race course and with trainers and owners to investigate each of this week's incidents.
Open Image Modal
8-year-old Pont Alexandre pictured here at a race day in Co. Kildare, Ireland
Niall Carson/PA Wire
Jenny Hall, Chief Veterinary Officer of the BHA, said: “First and foremost our thoughts today are with the connections of Long Dog and Montdragon, in particular all of the staff who will have loved and cared for the horses during their lives.
“It is notable that four of the fatal injuries incurred this week were not related to a fall over a hurdle or fence. Horses are at risk of serious injury throughout their lives, regardless of the type of equestrian activity they participate in.
“We will work with Cheltenham to assess all of the incidents that took place this week. We have a good relationship with the RSPCA and World Horse Welfare, and, as always, we will work with them to ensure we continue we do all we can to make racing as safe as possible.”
Tap and swipe to begin slideshow below
Cheltenham Festival 2016
(01 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: A racegoer celebrates after a race during Gold Cup day at the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England.The four day annual jump racing event sees jockeys compete for a piece of the 4.1 million GBP of the prize money. (Photo by Ben Pruchnie/Getty Images) (credit:Ben Pruchnie via Getty Images)
(02 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Victoria Pendleton smiles after riding Pacha De Polder to finish fifth in The St James's Place Foxhunter Steeple Chase Challenge Cup during the Gold Cup Day of Cheltenham Festival at Cheltenham racecourse on March 18, 2016 in Cheltenham, England.(Photo by Alan Crowhurst/Getty Images) (credit:Alan Crowhurst via Getty Images)
(03 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Racegoers watch a race on a large TV screen during Gold Cup day at the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England.The four day annual jump racing event sees jockeys compete for a piece of the 4.1 million GBP of the prize money. (Photo by Ben Pruchnie/Getty Images) (credit:Ben Pruchnie via Getty Images)
(04 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Bryan Cooper riding Don Cossack win The Timico Cheltenham Gold Cup Steeple Chase during the Gold Cup Day of Cheltenham Festival at Cheltenham racecourse on March 18, 2016 in Cheltenham, England.(Photo by Alan Crowhurst/Getty Images) (credit:Alan Crowhurst via Getty Images)
(05 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Victoria Pendleton (red cap) riding Pacha Du Polder jumps during the St. James's Place Foxhunter Chase Challenge Cup as part of the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England. (Photo by Mike Hewitt/Getty Images) (credit:Mike Hewitt via Getty Images)
(06 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: (EDITOR'S NOTE: Image was created as an Equirectangular Panorama. Import image into a panoramic player to create an interactive 360 degree view.) General view as riders jump during the Johnny Henderson Grand Annual Chase Challenge Cup (Grade 3 Handicap) as part of the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England. (Photo by Mike Hewitt/Getty Images) (credit:Mike Hewitt via Getty Images)
(07 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Bryan Cooper on Don Cossack celebrates victory entering the winners enclosure after the Timico Cheltenham Gold Cup Chase as part of the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England. (Photo by Michael Steele/Getty Images) (credit:Michael Steele via Getty Images)
(08 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: The sell out crowd watches the racing during the Gold Cup Day of Cheltenham Festival at Cheltenham racecourse on March 18, 2016 in Cheltenham, England.(Photo by Alan Crowhurst/Getty Images) (credit:Alan Crowhurst via Getty Images)
(09 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Bryan Cooper on Don Cossack celebrates victory after winning the Timico Cheltenham Gold Cup Chase as part of the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England. (Photo by Michael Steele/Getty Images) (credit:Michael Steele via Getty Images)
(10 of11)
Open Image Modal
CHELTENHAM, ENGLAND - MARCH 18: Bryan Cooper on Don Cossack celebrates victory after winning the Timico Cheltenham Gold Cup Chase as part of the Cheltenham Festival at Cheltenham Racecourse on March 18, 2016 in Cheltenham, England. (Photo by Mike Hewitt/Getty Images) (credit:Mike Hewitt via Getty Images)
(11 of11)
Open Image Modal
Bryan Cooper (L) celebrates on Don Cossack after his victory in the Cheltenham Gold Cup on the final day of the Cheltenham Festival horse racing meeting at Cheltenham Racecourse in Gloucestershire, south-west England, on March 18, 2016. / AFP / ADRIAN DENNIS (Photo credit should read ADRIAN DENNIS/AFP/Getty Images) (credit:ADRIAN DENNIS via Getty Images)