To save Frances Leatherman's life, a medical team needed to put her in a state very much like death.

Although Leatherman wasn't familiar with all the technicalities of open-heart surgery, development of a technique for cooling the blood--to drastically lower heart and body temperature --permitted her to approach the operation with sang froid.

Fifteen years ago, one of every five heart-valve replacement patients died. Those like Frances Leatherman, in their late 60s, were still operated on because they would have died without the operation--but they often died with it. Reducing the heart's temperature during the operation reduced the damage such surgery inflicted on it.

Leatherman's surgery would not have been possible at all without the development of the heart-lung machine, a relatively simple device that siphons blood from the body, puts oxygen in the blood and then pumps the blood back into the body. The machine has the capacity to heat or cool the blood, allowing the operator-- known as a perfusionist--to lower the patient's temperature from the normal 98.6 degrees Fahrenheit to 68 degrees, and later warm the blood.

When Nevin Katz enters the operating room at 7:13 a.m., 15 minutes after Leatherman, he is the last of the 11-member surgical team to arrive. Leatherman is still conscious, but sedated. Tubes have been inserted in her veins to monitor her vital signs. After being told that the tubes have been inserted, Katz greets Leatherman warmly, saying: "We're putting you to sleep. See you tonight."

In the next 40 minutes, Leatherman's body and legs are scrubbed with antiseptic soap, painted with antiseptic, covered with an adhesive plastic and then draped with sterile cloths--all to reduce the chance of infection. A blue curtain separates Katz and those assisting him around the operating table from Leatherman's face, so that her heart appears to independent of the body. The little of her body exposed is a ghastly yellowish-orange from the antiseptic.

I think we're set," Katz says, poised over Leatherman's chest. "Okay. Here we go." While Mozart's Piano Concerto No. 5 plays on a small tape recorder, Katz makes the first incision--a foot-long gash from Leatherman's navel upward, exposing the chest cavity. Katz then quickly takes an electric saw and cuts through the sternum in about 10 seconds. Smoke rises from the body cavity as Katz takes an electric needle to cauterize blood vessels he has ruptured. In roughly 10 minutes, Leatherman's beating heart is exposed.

Katz and David Pearle, Leatherman's cardiologist, already have established that despite her serious coronary artery disease, Leatherman is a poor candidate for coronary bypass surgery to correct the problem. The plaque that is blocking her coronary arteries is diffuse, rather than concentrated at one point. Katz confirms that diagnosis as he examines Leatherman's heart.

At this point, Katz has to make a major decision. He believes--but isn't certain-- that Leatherman's aorta is 23 millimeters in diameter. That would be a standard size and would accommodate the replacement valve he intends to substitute for the defective one. But Katz won't know the aorta's diameter with certainty until he cuts it open. At that point, Frances Leatherman will be on the heart- lung machine, and although a patient may be kept on the machine safely for hours, the less time that elapses on "bypass," the better.

Katz decides to prepare a Dacron patch in case the aorta is too small. If he needs the patch, it will be ready without prolonging Leatherman's time on bypass.

As he works, Katz quietly gives orders to the four persons assisting him. To Katz's left is Dr. John English, a first-year resident. On Katz's right is Eileen Mattei, the scrub nurse, responsible for handing Katz whatever tools he needs during the operation. To his left across the table is Dr. Linda Huang, a fourth-year surgical resident. Next to her is, Mark Mauer, a third-year medical student.

It takes about 20 minutes for Katz to prepare the Dacron patch. At 8:55 he changes glasses, putting on a pair with three and a half- power telescopic lenses attached to the normal corrective lenses, giving him a magnified view of the area where he is working. In 10 minutes, after Katz has inserted tubes through holes he has prepared in her heart, Frances Leatherman is "on the pump." At this point, Leatherman's heart keeps beating while Katz and John O'Connell, the perfusionist running the heart-lung machine, check its performance, and hers.

Once assured that everything is working properly, Katz tells O'Connell to inject a cold solution with a high potassium content into the heart. The potassium will stop the heart. O'Connell has already started chilling her blood to lower the body's temperature.

Because Leatherman's heart will be getting almost no blood during the time she is on bypass, its oxygen supply will be limited. Chilling the heart drastically reduces its metabolism, cutting down on its oxygen needs and thereby the risk of damaging heart tissue. With the aorta clamped, Katz pours a cold saline solution directly on the heart. A monitor shows the heart's temperature is less than 50 degrees Fahrenheit. At that temperature and with periodic administration of the potassium solution, heart function is impossible. The continuous electrocardiogram displayed on a wall video terminal is flat, indicating no heart function. Under a different set of circumstances, that flat horizontal line would indicate a crisis. Now it means that everything is as it should be.

Katz cuts open the aorta, tilting his head so that the miniature spotlight shines into the opening. He announces, to no one's surprise, that Leatherman has a "severely diseased tricuspid valve." The three leaves of the valve are heavily encrusted with calcium, quite possibly the result of a bout with rheumatic fever 40 years ago. The calcium deposits stiffened the valve and made it heavier, creating a severe burden on Leatherman's heart.

Katz cuts a strip of gauze and packs it below the valve to catch tiny but potentially lethal pieces of calcium that might flake off when he removes the valve. With a forceps he holds up one such piece, about the size of a dust speck. In the bloodstream, this calcium flake could cause a stroke, or death. Five minutes later, Katz is still picking out pieces of calcium. "This is just sort of a painstaking part of the procedure but a very important one," he says. When he finishes, Katz takes a pair of surgical scissors and cuts out each of the three leaves of Leatherman's diseased aortic valve, trying to clear a space for the sutures that will hold the new valve in place.

At 9:30, 96 minutes into the operation, Katz takes a gauge and measures the diameter of Leatherman's aorta. His estimate is correct: The aorta is a size 23, perfect for the valve that lies waiting to be implanted.

The valve, from a pig's heart, is natural tissue. (The valve will cost Frances Leatherman $2,240, part of a hospital bill that will total approximately $36,000, most of it covered by insurance.) Man-made valves also are used. Each type has its advantages and drawbacks. Mechanical valves are often used in younger patients because they seem to wear better than tissue valves. Mechanical valves require the recipient to take anticoagulant drugs forever. In the natural valve, porcine tissue has been sewn to Dacron mesh and the entire valve has been mounted and sewn on a metal ring. This valve functions much the same way the human valve does--permitting blood to flow from the left ventricle. The motion of the blood coming back between pulsations of the chamber catches the leaves of the valve and pushes against them, causing them to close.

Using suture needles handed to him by Mattei, Katz begins the tedious process of sewing the valve into place. Each polyester thread has a Teflon pledget, or stopper, at the end of it to keep the thread from pulling through the tissue, an important precaution in Leatherman's case because she takes steroids. The steroids control lupus--a disease that destroys connective tissue and often attacks the body's vital organs. But the steroids also weaken the tissue, making it more susceptible to tearing.

The suture thread itself is color-coded, in six separate colors, so Katz can keep track of his progress more easily. After passing the needle through the wall of the aorta, Katz brings the thread through the valve.

After six double strands of thread are sewn to the aorta and valve, Katz turns the valve slightly, while Huang holds the loose thread ends. As Katz finishes the next set of six sutures, Mauer takes the loose ends. English takes the third set. In all, Katz circles the valve with 18 double strands of silk thread. When finished, Katz pushes the valve slowly down the threads until it is seated in the spot where Leatherman's natural valve had been. Once the valve is seated, Katz ties five knots in each thread, pushing the knot down with his left index finger, moving back and forth from side to side among the threads to balance the tension and form a tight surface.

After checking again for any gaps where the valve sits, Katz begins closing the aorta, sewing through Teflon strips placed on either side of the incision, once again to buttress the sutures.

At 10:31, Katz tells O'Connell to begin rewarming Leatherman's blood. O'Connell does so. Eight minutes later, Katz removes the clamps blocking blood from the heart, giving it the first significant blood supply in almost 90 minutes. After waiting five more minutes for the body and heart to warm, Katz takes two paddles attached to an electric charger and attempts to restart her heart by shocking it. Something isn't working properly, however. Current isn't passing through the paddles. After two unsuccessful attempts, Katz quietly--with no sign of irritation--sends for another set of paddles. The second set appears to work no better. Still not concerned, because the heart can restart spontaneously as it warms, Katz sends for another machine. O'Connell suggests to Kim that he check a switch on the machine. On the third attempt, with Katz gently holding the paddles above and below the heart, electrical contact is made and Leatherman's heart starts beating.

As the machine continues rewarming Leatherman's blood, Katz is busy connecting temporary wires to the heart to monitor its performance in the next few days and to permit attachment of a temporary pacemaker if the heartbeat becomes irregular. At 11:18, about two hours and 15 minutes after going on the bypass machine, Frances Leatherman is off it, with a new valve in place--her heart pumping at a rate of 95 beats a minute.

Leatherman passes the final potential crisis point-- administration of protamine, a drug that reverses the effects of an anticoagulant that Leatherman was given earlier. Katz sends a nurse to tell Leatherman's family that she's in good shape.

O'Connell, now free from watching the tubes and pumps that kept Leatherman alive, pronounces the operation "routine." The only hitch that develops is that Mattei cannot locate one gauze sponge. She has recounted several times and still comes up one short. Leila Cabrera, the nurse responsible for supplies during the operation, has dumped each of the waste cans in the operating room and examined their contents, but cannot find the sponge. Katz is told. He does a careful visual inspection of the chest cavity to make sure the sponge is not there. As an added precaution, he puts his hands behind Leatherman's beating heart but cannot feel it there either.

The chest cavity is bathed with a warm antibiotic solution to prevent infection. Katz inserts six strands of No. 5 gauge wire through Leatherman's sternum as he begins the careful process of ou closing up the incision. By 12:20, Leatherman's chest is closed. She remains on the operating table until a technician arrives and makes an X-ray, a further precaution to make sure that the gauze sponge, which has an X-ray detectable strip on it, has not been left inside. After inspecting the X-ray himself, Katz supervises Leather- man's transfer to a gurney for her trip upstairs to the intensive care unit on the sixth floor. At 12:56 p.m., she is wheeled out the door. The operation so far is a success. The patient is alive and doing well.