Question: How do you give a 448-pound gorilla an EKG?
Answer: With a lot of help.

It takes ten people to lift a sedated hulk named Mopie onto the operating table at the National Zoological Park hospital. Actually, the 24-year-old silverback is getting much more than an electrocardiogram. For over an hour he will be put through some of the most sophisticated heart tests we have, including an exam with a transesophageal ultrasonic scope, part of a Doppler echocardiograph machine.

The scope is a silvery L-shaped tube, hardly a foot long, and it costs $48,000. It is hand-built, with 64 crystals that can be fired in phased sequence to vibrate and thus send sound waves into the heart; the waves that bounce back are digitally reconstructed into a video image. Inserted into the esophagus next to the heart, the instrument provides an extraordinary picture of that organ, its valves, the aorta and everything else, as it pumps away. What we have here is a charming switch: the latest developments in human medicine being used to benefit animals.

"Cardiovascular disease is a significant problem in orangutans and gorillas, especially male gorillas," Dr. Richard Cambre, head of the Zoo's Department of Animal Health, tells me. "We've done all nine of our orangutans and now are working on the nine gorillas with echocardiograms, blood pressure exams and blood workups for cholesterol and lipid levels."

Though zoo animals live longer than wild ones as a rule-35 years is the average age for gorillas; the record is 54-they tend to develop heart trouble. No one knows just why. Is it hypertension? Arteriosclerosis? And why the high cholesterol? Though the Zoo provides the apes with a diet that is as close as possible to what they would eat in the wild, are the apes missing some trace item, some leaf or plant that they find in the lowlands of Zaire and Cameroon?

"These exams will give us baseline stats," Cambre says, "so we can follow them in later years. One thing: we don't have heart data on gorillas while they're awake. We might be able to train orangutans to accept a blood pressure cuff, but gorillas, I don't know."

They are not ideal patients. When Dr. Lucy Spelman, associate veterinarian at the Zoo, approached Mopie earlier this morning with the dart gun that would anesthetize him, Cambre recalls, "he figured out what was going on before she had a chance to fire the dart, though he'd never seen this particular type of equipment before. He knew what was going to happen to him." So Mopie produced from the source a gigantic handful of fresh gorilla manure and hurled it at Dr. Spelman, spattering her from hair to heels.

Undaunted, she is in the operating room working away on Mopie with the rest of the doctors when I arrive. She has wiped the stuff off her glasses but is otherwise concentrating on what she has come here to do. All in a day's work. The place has a pungent smell, somewhat like a bad case of halitosis. The vets tell me this is the normal scent of a gorilla when he's scared.

The dart, fired from an air pistol, goes into the leg muscles and puts a gorilla down in 15 minutes or so. After that he is kept under anesthesia with isoflurane gas, inhaled through a tube.

Now Mopie lies there with his silverhaired knees splayed and his giant paws curled like a sleeping child's fingers. A transducer clipped to his tongue tracks his blood oxygen saturation and pulse rate. His eyes are slightly open. The doctors bustle around him in their surgical masks and gloves, taking notes, checking the video monitors, moving probes about on his vast chest.

When I ask how she got into doing this, Dr. Spelman says simply that she always wanted to be a zoo vet. She was in private practice but prefers the variety of experience in a zoo. In one day she may help with a cardiac workup on a gorilla, do a root canal on a Sumatran tiger, take blood from a sea lion.

As Mopie's heart thumps away in living color on the Doppler machine, a frighteningly accomplished trunkful of electronics costing six figures and loaned by Hewlett-Packard as a friendly gesture, I talk to Dr. Steven Goldstein, one of three Washington cardiologists who have given up this Sunday and volunteered to help. I ask if Mopie's heart rate of 123 beats per minute, duly recorded on the monitor, is very bad.

"It would be bad for a human but might be not so bad for an ape. This may be mild for him." Goldstein does, however, see what appears to be a problem in the main pumping chamber, the left ventricle. Normal human ventricles eject 60-70 percent of the blood in a given contraction. In orangutans, the efficiency is down to 55-65 percent. Mopie's is as low as 35 percent.

"I think it's abnormal, but I've only seen 10 or 11 great apes," says Goldstein, who has been volunteering at the Zoo since September 1995. "He's the second gorilla that I've seen with this condition. His father died at 37 of a heart problem, but then his father was born in the wild. Apes do live artificially long in captivity."

The beauty of the Doppler machine, National Zoo primates curator Lisa Stevens tells me, is that you can literally watch and videotape the heart at work. A conventional heart x-ray might be obscured by the ribs and, besides, is two-dimensional and static. When the ultrasonic scope is inserted, you can see everything in motion, even the aortic valve opening and closing.

Stevens came to the National Zoological Park straight from Michigan State, 18 years ago. "I thought I'd do this for a few years, but then I realized that this was it. I started with cats, then bears, seals and sea lions. You become specialized eventually, but most people are very versatile. You work with all the animals, from elephants to fish. And you appreciate and respect them all."

Dr. Cambre, who came here two years ago after 15 years at the Denver Zoo, says that being a zoo veterinarian gets into your blood. "Animal personalities are fascinating. We have PhD curators here and a keeper staff that's mostly college educated. We depend on them to report unusual behavioral patterns for individual animals to us. Sometimes these are early warning signs of illness. It takes a team effort to figure out what's going on." Without an owner to tell them what an animal's problem is, Zoo people have to rely on their own close observations. Is an animal eating well? Defecating normally? Moody? Under stress?

On another of my visits to the Zoo, Azy, a large male orangutan, spotted Cambre as we strolled past. Azy rushed back and forth in his cage, pushing a huge barrel before him in an impressive display of power. "It's a lot of bluster," Cambre said. "He's trying to intimidate me. He knows who I am. He knows who's going to win if I get my dart gun. So he's bluffing. Of course, if I was stupid enough to wander into his cage, he'd kill me. They're forgiving up to a point. But they don't like us, because if they're sick we've got to dart 'em."

After the heart exam, as Mopie lies on his back, half covered by a blanket and breathing peacefully, Dr. Spelman cleans the gorilla's wicked-looking teeth with dental tools. Yes, even apes are prone to cavities and gum disease. Now Mopie is being unplugged from the monitors and transferred to an x-ray table for a complete set of pictures. Even moving him from one table to another takes a half-dozen people hauling on the heavy canvas netting he's lying in.

"We'll take him off anesthesia when he's back in a cage," explains Stevens. "He'll recover pretty fast. He'll be groggy for the rest of the day, but awake and eating. He might be a little cross. He's into that role of being the big dominant male. Mopie can be sullen, but he has his light moments. By tomorrow he'll be back to normal."

The team struggles through narrow doorways with Mopie and deposits him in a van for the trip back to the ape house. There they tug and push him through barred passageways to a cage, where the anesthesia tube is removed. Immediately he begins to clear his throat, sounding exactly like my father in the morning. In a minute he starts to move, and the staff leaves to give the same round of tests to another gorilla.

I hear some serious screams and the pounding of bare feet as a large female named Mesou flees down a runway. Following her, holding a long dart gun, comes the intrepid Dr. Spelman in clean coveralls, her brown hair pulled back in a ponytail. She moves with deliberation, intent and calm.

The CO2 gun pops. "There," she says. "That was a good one." Mesou sits down with a philosophic grunt.

By Michael Kernan