Guiomar Novaes, 83, an internationally known pianist who had toured extensively in the United States and Europe as well as South America, died of a heart attack Wednesday in Sao Paulo, Brazil. She had suffered a stroke in January.

She was born in the small Brazilian town of Sao Joao de Boa Vista, near Sao Paulo, where she was educated. She gave her first concert at the age of seven.

Mme. Novaes studied at the Paris Conservatory in France, and at the age of 15 won a first prize. One of the judges was the composer Claude Debussy. He wrote of her:

"She has all the qualities to be a great artist, eyes which are transported by the music, and the power of total inner concentration, as are characteristic in artists."

Mme. Novaes made her United States debut in New York in 1915. She gave more than 500 concerts and recitals in this country and made frequent appearances at Constitution Hall here. Over the years, she had performed with the major orchestras of the Americas and Europe, including the National Symphony Orchestra here.

She was the widow of Octavio Pinto, a Brazilian civil engineer, composer and pianist who died in 1950. They had two children, Luiz Octavio and Anna Maria.