Gunther Karl Kessler, Annandale pharmacist for more than 20 years and former vice president of the Commonwealth Doctors Hospital in Fairfax, which he helped establish, died Wednesday at his home in Ruckersville, Va., after a heart attack.

Mr. Kessler was born and reared in Koblenz, germany. In 1937, two weeks before he was to report for duty with the German army, he left Germany and joined a brother who was living in Washington.

During World War II, he served as an American counterintelligence agent in Europe. He returned here after the war, and graduated fromGeorge Washington University's school of pharmacy in 1953.

In 1958, after working as a drugstore pharmacist, he went into business for himself. He operated pharmacies in the Annandale Doctors Building which he helped establish, the Annandale Medical Building and Commonwealth Doctors Hospital before opening Kessler's Pharmacy Inc. in Annandale in 1963.

Mr. Kessler also was a founder of the Sleepy Hollow Manor Nursing and Convalscent Home in Annandale and was associated with the Northern Virginia Doctors Hospital.

He was a director of the Potomac Bank and Trust Co., a director of E-Z Communications Inc. in Fairfax, and a past president of Virginia Medical Supply Inc.

In 1961, Mr. Kessler donated materials to establish the Fairfax Hospital poison control center, including his poison control kit and his personal library on poisons and some 300 antidotes.

Mr. Kessler had been semiretired since 1974 for reasons of health. He was a fourth-degree Knight of Columbus.

He held a number of professional memberships, and in 1977, was named pharmacist of the year by Virginia Pharmaceutical Association. In 1978, he received the George Washington University alumni achievement award.

In recent years he, and his wife, Ingeborg, and a son, Peter, lived in Ruckersville at their home, Sauerkraut Chalet, a name chosen by Mr. Kessler because of both his and his wife's German origins.

Besides his wife and son, survivors include four sisters, Katie Adamson, and Lina Allegra, both of Takoma Park, Anne Marie de La Rue, of Hyattsville, and Mitzi Diehl, of Port Republic, Va.