The shape of the heart, as much as the shape of the clothes, was the focus of yesterday's 31st annual benefit luncheon at the Washington Hilton. A record turnout of 1,600 guests watched as models, led on stage by teen-age dancers and acrobats, jogged, jumped rope and generally exercised their way around the ballroom runway on behalf of the American Heart Association.

I. Magnin presented the fashion show which featured sports clothes to keep your heart in shape, minimal bathing suits (that showed off what good shape the models were in), executive lady's suits, dotted prints, designs in (often shocking) bright colors, and evening wear.

The audience clearly preferred the lady-like dresses in navy primly trimmed with white collar and cuffs, part of a sequence in which models George Weeks and Alan Cephus in sailor suits tried, mostly unsuccessfully, to pick up the female models. (The sailors were typical of the minimal "props" that made the show entertaining without being distracting.)

There was some commotion at the end of the sailor sequence when a model appeared in an open-weave sweater with nothing underneath.A priest seated along the runway shielded his eyes when she passed.

As a warm-up to the luncheon, television sportscaster Glen Brenner demonstrated the cardiac stress machine but stepped off the treadmill after advising Georgetown University professor Dr. Samuel Fox that he had bronchitis.

Dr. Freeman Cary, attending physician for the House and Senate, was in attendance. He said that about half of all congressmen are now in a running program. He advised joggers who exercise outdoor in extremely cold weather to cover their mouths so as not to breathe in the cold air -- which he said "does something to the blood which can act adversely when it goes back to the heart." Cary warned that abrupt exposure to the cold -- when jogging or shoveling snow -- is most harmful, and suggested a ski mask to alleviate this risk.

The luncheon saluted Mamie Eisenhower, who had planned to attend but slipped in her kitchen last week, breaking her wrist and chipping a bone in her arm. "It's a tremendous inconvenience," said her sister Frances Moore. "It's her right hand and it is keeping her from doing her correspondence." CAPTION: Picture 1, 2, Jumping rope in terry shorts and jacket, above, and modeling a dotted dress; photos by John McDonnell -- The Washington Post