Ex-Olympic chief Juan Antonio Samaranch has been admitted to hospital after collapsing in Madrid on Wednesday.
After 21 years, Samaranch was succeeded by Jacques Rogge
Witnesses said the ex-International Olympic Committee (IOC) president fainted shortly before a fund-raising event organised by Real Madrid.
"The patient's situation remains stable and controlled," said Dr Raquel del Valle of the cardiology department at the Clinico hospital.
Samaranch, 87, was head of the IOC between 1980 and 2001.
He is now an honorary life president of the body which runs the Olympics and remains active in Spanish sports administration.
Head of Spain's Olympic committee
Alejandro Blanco, who is the head of Spain's Olympic committee, told Spanish radio that Samaranch felt unwell during the conference.
"Everything will be back to normal. We were afraid, but the situation is under control," said Blanco.
"He didn't feel very well. It is one of these problems he has regularly."
A colourful figure, Samaranch has recently been pushing Madrid's bid to host the Olympics in 2016.
In July 2001, on his 81st birthday, he was hospitalised in Switzerland for "extreme fatigue" the day after announcing the election of his successor, Belgian Jacques Rogge.
He was hospitalised again in Barcelona a month later for arterial hypertension because of the effort of organising the IOC Congress in Moscow.
Samaranch is often present at high-profile events such as Wednesday's, which was also attended by Real Madrid goalkeeper Iker Casillas and tennis player Rafael Nadal.