South African-born lawyer who had given up her legal career in New York to devote herself to philanthropy. She died on Jan. 31 at a hospital in Delray Beach, Fla., after falling from a horse while competing in a masters jumper competition at the Palm Beach International Equestrian Center in Wellington, Fla. She was 52. The cause was cardiac arrest brought on by a head injury, said Marisha Mistry, a spokeswoman for Liquidnet, an Internet stock-trading company founded by Ms. Heyman’s husband, Seth Merrin. Ms. Heyman had homes in Florida, Manhattan, Westchester County, N.Y., and Israel. Ms. Heyman graduated from the University of Pennsylvania in 1982, then spent another year in Israel before going to George Washington University Law School. In 1984, she transferred to Columbia Law School and graduated the next year. After two years of private practice, she became an assistant district attorney in Manhattan, prosecuting white-collar crime. She quit to devote herself to her family after her son Jonathan was born in 1994. Ms. Heyman began her career as an activist and philanthropist while at home with her children. She volunteered for Dorot, a Manhattan-based organization that serves the elderly, and became its chairwoman. One of her first steps in her Rwandan mission was linking up with the American Jewish Joint Distribution Committee, which had set up youth villages in the Americas, Europe and Africa.