Tributes have been paid to the two men who died after taking part in the Cardiff Half Marathon on Sunday.
Ben McDonald, 25, from Cardiff, and Dean Fletcher, 32, from Exeter, went into cardiac arrest after crossing the finishing line within three minutes of each other.
They both later died at the city's University Hospital of Wales.
Race organisers Run 4 Wales said a full review would take place but they were "100% satisfied" with the medical plan.
In a statement, the organisers said it was Mr McDonald's first time running the half marathon.
It said Mr McDonald, who worked at Cardiff International White Water centre ran with his girlfriend, two brothers, a brother-in-law and two sisters-in-law.
Mr McDonald's girlfriend Amy Stanton-Foo described him as a "happy, smiley, adventurous, loving person" in a social media post, while Ben Longhurst, manager of Cardiff International White Water said the team was "deeply saddened".
Father-of-one and former Cardiff University student Mr Fletcher, who was taking part in his second Cardiff race, had been part of a 350-person team which was raising funds for neuroscience, mental health and cancer research at the institution.
He was described as an "amazing husband and father".
The university's deputy vice-chancellor Prof Karen Holford said: "This news will come as a shock to everybody involved with Team Cardiff and indeed the whole Cardiff University community."
Run 4 Wales chief executive Matt Newman said: "This is a terrible tragedy for the families. Our heartfelt sympathies go out to the family and friends of both Ben and Dean.
"The medical team and emergency services reacted to this terrible situation with great speed and professionalism. Everyone connected with the race is devastated.
"We are in close contact with the families and will continue to support them in every way we can. We ask that their privacy be respected at this time."
About 20,000 people took part this year, on the race's 15th anniversary.
A review will now be carried out by race organisers, as is standard practice each year.
Mr Newman said: "We are 100% satisfied that there was nothing more that could be done by the team at Run 4 Wales or the medical professionals in place on the day.
"We have a team of 10 doctors in place and a huge deployment of medics and St John's Ambulance around the 13.1-mile course.
"There's an almost full A&E unit at the finish line and the medical team acted in complete professionalism."
Some people have taken to social media to say more should be done to help prevent fatalities at mass-participation events.
Devastated to learn of this. Condolences to all their family members. Medics towards the end of the course were pushed to their limits. Well done to the medics for their hard work. The course felt too crowded for safety this year.— Becca Milton (@becca_milton) October 7, 2018
Mr Newman said: "We know that on occasion people suffer with cardiac arrest but we absolutely make sure runners are informed of all the things they need to put in place from a health perspective.
"That includes training properly, being aware of any health issues and notifying us of those prior to the event."
Officials said this year's event was the biggest yet and could be worth more than £2.3m to the local economy.