Dean of Christ Church Cathedral Reverend Dermot Dunne has appealed for the return of the Heart of St Laurence O'Toole, which was stolen from the church at the weekend.
The 12th century preserved heart of the patron saint of Dublin was taken from the cathedral on Saturday morning.
The one-time archbishop was born Lorcán Ua Tuathail in Castledermot, Co Kildare in 1128 and died in France in 1180.
His heart has been preserved in Christ Church Cathedral since the 13th century and was a major pilgrimage site during the medieval period.
Speaking on RTÉ's Morning Ireland, Rev Dunne appealed for the return of the relic.
He said: "It has no economic value but it is a priceless treasure that links our present foundation with its founding father, St Laurence O'Toole."
Rev Dunne said the relic was stolen on Friday night or early Saturday morning.
The heart was kept in a wooden heart-shaped container within a small iron-barred case.
"It was bolted to the wall in a metal cage. Almost impossible to wrench it off the wall. It took quite a lot of effort to extract it from that cage," said Rev Dunne.
Gardaí have appealed to anyone with information to contact 01-6669400, the Garda Confidential Telephone Line on 1800-666111 or any garda station.
The Dean also revealed that a number of candles at the Cathedral were found to be lit when the theft was discovered on Saturday morning.
He said: "We have a peace candle, and we invite people to light candles during the day ... when staff were on their rounds, they found that it was lit already.
"And then in our Trinity chapel - our prayer chapel on the north transept - all the candles were lit there. It's quite confusing."