Alexander Zakin, a Russian-born pianist who was the longtime accompanist of the violinist Isaac Stern, died on Friday at St. Luke's-Roosevelt Hospital in Manhattan. He was 87 years old and lived in Manhattan. His family said he died of heart failure. Mr. Zakin performed with Mr. Stern in concerts around the world from 1940 to 1977, and they made several dozen recordings together.

The son of a violinist, Mr. Zakin was born in the Siberian city of Tobolsk and began studying piano at the age of 8 at the State Conservatory in St. Petersburg. He left his homeland in 1921 to continue his studies in Berlin, where he made his solo debut five years later.

He gave recitals and performed with chamber-music ensembles throughout Central Europe in the late 1920's and early 30's. After Hitler seized power in 1933, he found refuge in Luxembourg, where he taught members of the royal family and became a staff pianist with Radio Luxembourg.

He moved to New York in 1940 and soon afterward began collaboarting with Mr. Stern. In addition to performing in concerts and on radio and television, they appeared in ''Tonight We Sing,'' a film about the life of their manager, Sol Hurok. In 1983, CBS Masterworks released an album featuring Mr. Stern in tribute to Mr. Zakin.

Mr. Zakin is survived by his wife, the former Isabelle Drier, and a daughter, Nina Essey, both of Manhattan.