Christina Onassis, heir to the billion-dollar fortune of Greek shipping tycoon Aristotle

Onassis, suffered an apparent heart attack Saturday and died, officials said. She was 37.Onassis, whose famous father, stormy romances and huge fortune made her an international celebrity, was stricken at a country club swimming pool about 25 miles northwest of Buenos Aires, a doctor said.

Onassis, who was married four times and had a 3-year-old daughter, was the stepdaughter of Jacqueline Kennedy Onassis, widow of the late President John Kennedy who married Aristotle Onassis in 1968. (See today's Spotlight on A2.)

Dr. Hernan Bunge, a director of the Clin-ica del Sol Hospital in Buenos Aires, said Onassis was stricken at the weekend home of close friends Marina and Alberto Do-dero at the Tortuguitas Country Club.

Onassis fell ill as she prepared to go swimming about 11 a.m. in a pool at the home. She was taken to a country club first-aid station station for attention, then to the clinic, where she was pronounced dead at 3 p.m., he said.

The body of the heiress, whose frequent bouts with obesity were widely reported, was taken in an ambulance to the municipal morgue, where officials said an autopsy would be performed.

"No doctor can sign the death certificate without an autopsy because she was dead when she arrived," a police officer at the morgue told a crowd of reporters that jammed the entrance of the gray, three-story morgue.

Her body probably will be flown to either New York or Athens, said Marina Dodero.

Onassis arrived in Buenos Aires last month from Paris on one of her frequentvisits to the Doderos, an Argentine shipping family closely associated with her late father, the legendary Greek shipping magnate whose larger-than-life image is chronicled in books and films. Aristotle Onassis lived in Argentina as a youngman.

The heiress, who usually stayed with the Doderos at their downtown Buenos Aires apartment or in a luxury hotel, told reporters that she had come to help celebrate the 40th birthday of Marina Dodero. She was the godmother of one of the Do-dero's children.

Onassis inherited her father's shipping and real estate empire when he died in 1975 and was worth an estimated $1 billion.

She reportedly didn't get along with her famous stepmother. After Onassis died, his daughter and other members of the Onassis family reportedly offered Mrs.Kennedy Onassis a multimillion-dollar settlement to give up her rights to the Greek magnate's estate, news reports at the time indicated.

Onassis was married four times. She married French businessman Thierry Roussel, her fourth husband, in March 1984. She gave birth to her only child, Athena,in early 1985 and the couple filed for divorce eight months later.

Onassis' first marriage was in 1971 to Los Angeles real estate broker JosephBolker, who was nearly twice her 20 years. Their marriage ended after nine months. Her second marriage to Alexander Andreadis, the heir of another Greek shipping fortune, also was short-lived and ended in 1976.> Her third, perhaps most widely publicized marriage was in 1978, in Moscow toa Soviet civil servant, Ser-guei Kauzov. They were divorced less than two years later.

Onassis, a frequent visitor to Buenos Aires, maintained residences in Paris and St. Moritz, Switzerland. She also owned the Greek island of Skorpios in the Ionean Sea, which she inherited from her father. She also one time was toying with the idea of buying the island of Corisco, located in the Atlantic Ocean off the coast of central Africa, news reports indicated.

She was born Dec. 11, 1950, in New York City.