Ms. Heflin was best known for her featured roles in Mr. Altman's 1979 romantic comedy, "A Perfect Couple," and his 1982 film of Ed Graczyk's play, "Come Back to the Five and Dime, Jimmy Dean, Jimmy Dean," with an ensemble cast that included Sandy Dennis, Kathy Bates, Karen Black and Cher. She was in the Broadway production, which Mr. Altman directed as well, that same year.

Mr. Altman said in interviews that Ms. Heflin's unconventional, sometimes awkward beauty lent authority to her portrayal of average people in both films.

In "Come Back," she played a beleaguered character, pregnant for the seventh time, attending the reunion of a James Dean fan club 20 years after the actor's death. In "A Perfect Couple," she was a ragamuffin singer who, while living with a rock band, meets a paunchy middle-aged man (Paul Dooley) through a dating service and falls in love.

Ms. Heflin had small supporting roles in Frank Pierson's remake of "A Star Is Born" (1976), starring Barbra Streisand and Kris Kristofferson; "A Wedding" (1978), Mr. Altman's comedy of manners; and Martin Scorsese's "King of Comedy" (1982), starring Robert De Niro and Jerry Lewis.

She also appeared on the NBC soap opera "The Doctors" and in several made-for-television movies, including the concentration camp drama "Playing for Time" (1980), with Vanessa Redgrave, and "The Gentleman Bandit" (1981), about a priest wrongly accused of a series of armed robberies.

A cabaret singer as well, Ms. Heflin performed frequently at New York nightclubs. In a 1973 review of a cabaret performance, John S. Wilson of The New York Times praised her voice for its "warm, sunny glow" and "gospel song fervor."

Marta Michelle Heflin was born on March 29, 1945, in Washington, to Julia and Martin Heflin, a power couple of their day. Her mother was a journalist and theater producer and her father a public relations executive who was the brother of Van Heflin, the Hollywood actor. Information about survivors was not available.

In 1967, Ms. Heflin was in the chorus of a revival of the Lerner and Loewe musical "Brigadoon" at the City Center when she unexpectedly got her big break. Without rehearsal, she stepped into a prominent role as the soubrette Meg when the actress performing the part (without an understudy), Karen Morrow, came down with pneumonia.

In the next few years she landed roles in "Fiddler," "Hair" and "Salvation," a rock revue in the form of a Salvation Army-like revival meeting. "I played a nymphomaniac," Ms. Heflin said in a 1984 interview. Not the obvious kind but the quiet type, she added wryly: "The kind that wears Peter Pan collars."