Face of Nation : The male cyclist collapsed during the Wales Sportive event at Wisemans Bridge, near Saundersfoot, Pembrokeshire.
Paramedics were called just after 11:30 BST and he was treated at the scene before being taken to Morriston Hospital in Swansea.
Race organisers said he was being supported by his family.
“An athlete suffered a suspected heart attack on the course. He was treated at the scene and taken to hospital,” said race director Matthew Evans.
“We have notified the family and they are with him at the hospital. Our thoughts are with him.”
The road was temporarily closed while emergency services attended and competitors diverted.
More than 4,000 riders set off on the 42, 70 and 112-mile courses that started and finished in Tenby.
Organisers described the three-day event as “one of the most difficult but most rewarding events in Wales”.
Often used as training for those attempting Ironman Wales later in the year, the Wales Sportive is the second part of a challenging weekend that includes the 2.4-mile Wales Swim on Friday and Wales Marathon on Sunday.
This year’s event is the biggest since it began in 2010 with more than 10,000 competitors taking part.
