Athina Roussel, the billionaire heiress to the late Greek shipping tycoon Aristotle Onassis's fortune, married Brazilian equestrian champion Alvaro Affonso de Miranda in a sumptuous wedding held behind tight security in Sao Paulo on Saturday night, witnesses said.

Up to 1,300 guests from around the world attended the event on the lush grounds of an art museum in the smart Morumbi district. The couple exchanged vows around 10 p.m., and the party lasted until 4 a.m. Sunday, the witnesses said.

Divorced Miranda, 32, who is known by his nickname, Doda, was heard whispering, "You are everything to me," to his bride.

Athina's father, Thierry Roussel, who lost a fight with his daughter for control of her fortune and questioned Doda's motives for wooing one of the richest women in the world, did not attend. Athina, 20, was given away by the groom's father, Brazilian businessman Ricardo Miranda.

The marriage marks a bright spot for Athina in a life in which wealth has not prevented tragedy.

She has been known as the "poor little rich girl" in the world's celebrity media. Her mother, Christina, died at 37 in 1988 in Buenos Aires, when Athina was just 3, after a history of drug abuse and weight problems.

Athina met Doda, a two-time Olympic bronze medal winner, in Belgium in 2002 and romance blossomed over their shared passion for horses and riding. They live in a luxury penthouse in Brazil's biggest city.

The security operation for the wedding was worthy of a president, with more than 400 guards on duty at the Maria Luiza and Oscar Americano Foundation, a garden and museum that lies just a few miles from one of Sao Paulo's slums.

Guests were ferried to the venue in a convoy of limousines and had to pass through two security checkpoints. They were not allowed to bring in cell phones or cameras.

Once inside, they were greeted by music from a 40-piece orchestra. The gardens and marquees were decorated in a pastoral theme with bouquets of foliage and ivy wound around columns. Although Sao Paulo has been drenched with downpours in the past few days, the rain held off for the wedding.

The bride was dressed in a pearl-colored gown designed by Italian couturier Valentino. It had a long train, and she was bare-shouldered. She wore a Spanish-style mantilla headdress and low Chanel shoes.

The couple exchanged vows in an hour-long ecumenical service, since she is Greek Orthodox and he is Roman Catholic.

Doda's 6-year-old daughter, Viviane, from his former marriage was a maid of honor. Athina's half-sister, Sandrine, carried the rings.

Singer Debora D'Oliveira performed "O mio babbino caro" by Puccini and Gounod's "Ave Maria."

When the couple emerged for the party, they cut the cake, made a toast and locked into a slow dance. A DJ spun Brazilian pop hits and other numbers including the Bee Gees' "Stayin' Alive."

Some 1,000 bottles of Veuve Cliquot champagne were laid in as well as a 2002 Bordeaux. The bars also served Brazilian caipirinha cocktails.

The French cuisine included chilled soup, salmon, shrimp in artichokes and palm, and a veal on risotto.

The couple asked guests to contribute to a charity instead of giving gifts. After the wedding they left for a Sao Paulo hotel and will honeymoon at a secret location.

The French-born Athina is the sole heiress to her late grandfather's fortune, worth at least $1 billion. Her property includes the Greek island of Skorpios, where Onassis married Jacqueline Kennedy in 1968.

Athina turns 21 next month and is embarking on a struggle for control of the billion-dollar Onassis Foundation charity. Its trustees have decreed she is not Greek enough to head it.

Doda has encouraged her to improve her Greek credentials, according to media reports. She has said she wants to ride for Greece in the next Olympics.