Ruth Saunders Braitberg, who performed professionally as Natasha Rubinstein, and who was the principal cello with the Muny Orchestra and the Webster University Symphony Orchestra, died unexpectedly of a heart attack, Saturday, Jan. 2, 2010, while out walking near her Olivette home. She was 59.

Ms. Rubinstein’s mother, Ruth Saunders, is a pianist and a retired professor of music at St. Louis University. Mrs. Saunders said that her daughter was involved in teaching and playing her music, and that she did everything “with a full heart.”

Ms. Rubinstein was born Oct. 13, 1950, in Boston. Her family moved to St. Louis when she was a child. She was a graduate of University City High School and Washington University. Her first instrument was the piano, and she took up the cello at age 8. She grew up playing with the University City Orchestra.

Ms. Rubinstein worked for several years in the New York area, and returned to St. Louis where she became a freelance cellist and teacher. In addition to her serving as the principal cello with the Muny, she also performed at the Repertory Theatre, the Fox Theatre and other venues.

She performed chamber music with the Eden Trio and other ensembles. Ms. Rubinstein, and her husband, Michael Braitberg, were co-owners of a booking agency, Elegant Ensembles, which provides musicians for weddings and other events.

Ms. Rubinstein was active in the Musicians’ Association of St. Louis and took an active part in union contract negotiations. Vicky Smolik, association president, praised Ms. Rubinstein as “a fine musician,” and said she was “well-thought of, both in the theater community and the classical musical community in town.”

A memorial service was held last Wednesday at the Berger Memorial Chapel, 4715 McPherson Avenue.

Burial was at B’nai Amoona Cemetery.

In addition to her mother and husband, Ms. Rubinstein is survived by three children, Alexander Braitberg; Tova Braitberg, a violinist and violist; and Gabriel Braitberg, a harpist, all of St. Louis County; a sister, Catherine Saunders Dunphy of Denver; and a brother, David Saunders of Boise, Idaho.

Memorial contributions may be made to a charity of the donor’s choice.