Sara Blumenthal, wife, mother, student and full-time government clerk was trying to do it all.

Barely 40, she was on her way to new womanhood, A-type personality and all. But a not-very-funny thing happened on the way to Sara Blumenthal's self-fulfillment.

She had a heart attack.

Except for her age, it shouldn't have been such a surprise. There was plenty of heart trouble in her family on both sides. Her father had died of a heart attack.

Besides, she had been a two-pack-a-day smoker for some 23 years -- she had stopped, but only a year before.

And finally, she didn't have chest pains. She had a backache.

Nobody thought it was a heart attack. Not the hospital in Silver Spring, nor her doctor . . . They gave her muscle relaxants and told her to take it easy.

On the third day when the pain had not shown any sign of abating, her doctor did an electrocardiogram, mainly as a last resort.

"He came into the office," Blumenthal recalls, "white as a ghost, and said, 'You're having a heart attack,' and I laughed and said, 'You're kidding,' and he said, 'Don't go home. Don't pack. Have your husband take you directly to the hospital . . .' "

For Sara Blumenthal it was the ultimate downer.

She was depressed, discouraged, terrified of her own heartbeat . . . Despite the support of her husband and two daughters, she felt her life was effectively over.

For 18 months she wouldn't walk down the stairs to her basement.

She wouldn't go out for fear something would happen.

She was classically representative of women who have heart attacks, especially before menopause. Although statistics do not uphold the conventional wisdom that more women than ever are having cardiovascular incidents, studies do show that the ones who do -- A-types (competitive, driving) -- have a poorer chance of full recovery.

It looked like Sara Blumenthal was going to be another statistic.

Then she found Paula Cox.

Cox is a certified physician's assistant. She was coordinator of cardiac rehabilitation at the George Washington Medical Center, and is now director of Cardio Rehab Center in Chevy Chase, Md., the only private center of its type in this area.

Sara Blumenthal heard about it from a "little lab assistant" in her doctor's office.

The heart specialist at the Washington Hospital Center, said, "Sure," when Blumenthal asked if he thought it was a good idea. Her own doctor said, " 'Absolutely not.' He said, 'No, you're doing okay,' and I said, 'No, I'm not doing okay' . . . I was very frightened, afraid to run, even for a bus or an elevator."

Whether or not exercise does prevent heart attacks, or a recurrence of heart attacks, is still unproven. But, says Paula Cox, "We do know it exercise will probably help you keep your coronary risk factors under control, and it's definitely going to make you feel better.

"Studies have been conclusive that in heart patients who have been exercising regularly, levels of anxiety and depression -- common after heart attacks -- are decreased, and those who exercise are living healthier and more productive lives faster than those who don't."

Of course nobody, especially no heart patient, should undertake any exercise program without a physician's approval. It should be noted that Blumenthal's physician didn't forbid her from the program. He just didn't think she needed it.

Cardio Rehab is typical of several hundred similar outfits springing up in hospitals and clinics throughout the country. Under trained supervision, cardiac patients, usually referred by physicians two or three months after their heart attacks, engage in individually tailored exercise programs to bring their heart rates up to their own aerobic level (roughly 70 percent of stress-causing rate), followed by a dramatic drop in rate when at rest.

Cox has around a dozen physicians who are consultants and oversee the whole operation. There is monitoring equipment, crash carts for emergencies and personnel thoroughly trained in cardio-pulmonary resuscitation.

Although some physicians are uncertain about the program's benefits -- especially for women -- insurance companies endorse it in the best way they can: They pay some or all of its costs.

When Sara Blumenthal came in, Cox recalls, she figured she had trouble.

"Let's put it this way," says Blumenthal, "I never believed in exerting myself."

"She was so deconditioned," says Cox, "her muscles were mush."

The first thing Cox told Blumenthal to do was walk up and down stairs for five minutes without stopping.

"Are you crazy?" countered Blumenthal, "I'll have another heart attack . . ."

She refused for the first 12 weeks of the program. Then Cox said, "Listen, I'll go down your basement steps with you. She said, 'You don't understand. When I can go up and down the stairs, all I get for it is to do the laundry. My daughter has been doing the laundry for a year now . . . and the minute my family sees me going up and down the stairs, well, ZONK, it'll all fall to pieces.' "

"I finally did it," says Blumenthal. "I did 260 stairs in 4 1/2 minutes. So the next time I had to go out and there were 10 stairs and I'd tense up, I'd tell myself, 'You idiot, you just did 260 . . .' "

The trouble was, she grins, "I blew my cover.

"The other day I asked my husband to get something for me and he said, 'Get it yourself.' "

Sara Blumenthal is back in school full time, doing volunteer work for Cardio Rehab -- for whom she is an ardent advocate -- and lifting small weights.

She was shaving her legs recently and thought she'd found a tumor.

It was a muscle.

Cardio Rehab Center has contracted with the National Capital YMCA to set up a cardiac rehabilitation program, now scheduled to get underway early next year. For information on that program and on Cardio Rehab itself, phone Paula Cox at 654-0434.

For a free listing of all cardiac rehabilitation programs in the Washington area, send a self-addressed, stamped envelope to Cardio Rehab Center, Suite 740, 5530 Wisconsin Ave., Chevy Chase, Md. 20015.