How did the cartoonist Kliban, Bernard "Hap" die in 1990?

Answer 1

According to this site, he choked on a hairball:

http://www.msu.edu/~daggy/cop/bkofdead/obits-ki.htm

Page down to find his name. However, his actual cause of death was heart surgery:
http://www.vipatients.com/

See B. Kliban (occupation: cartoonist)

Answer 2

Cancer.
From an article about Bill Bixby:
"In late 1992, friends introduced him to the artist Judith Kliban, widow of B. Kliban, a cartoonist who had died of cancer."
Not sure what kind of cancer, though.