ITHACA, N.Y. -- When their veterinarian said Shasta could die within the year, the Hoffmans were devastated and they faced a tough decision.

Should they give up the 6-month-old German shepherd for research into a canine disorder that may parallel some forms of human Sudden Infant Death Syndrome (SIDS)? Or should they let their own kids enjoy the seemingly healthy puppy while she lived?

"It was really hard," recalls Robyn Hoffman of Antioch, Calif. "Shasta was our 'baby.' We had just taken her to the vet clinic to be spayed. She seemed fine. Then they called and said that when they gave Shasta anesthesia, they found an irregular heartbeat."

Cardiac arrhythmias in sleeping dogs are pointing to one possible cause of SIDS in humans. Researchers at the College of Veterinary Medicine at Cornell University have found that some German shepherds have an inherited abnormality that predisposes them to sudden death at an early age.

Hearts in German shepherds with this abnormality function normally during their waking hours. The dogs run, jump and fetch with the best of them. Only when they lie down and go into REM (rapid eye movement) sleep do the potentially fatal arrhythmias -- including the wildly racing heart beats called tachycardia -- begin.

Some young dogs never awake. In a provocative similarity to human SIDS, other dogs "outgrow" the risk of death. "Just as with babies who succumb to SIDS, routine postmortem examinations do not reveal a cause of death," said N. Sydney Mo•se, D.V.M. A veterinary cardiologist and associate professor of clinical science, Mo•se heads the Cornell dog study, with funding from the National Institute for Child Health and Human Development.

"We hear reports from German shepherd owners and breeders across the U.S., as well as Great Britain, Italy and France," she said. "Some are losing one pup in a litter; in other litters, they all die between 4 and 8 months of age." So Mo•se asked breeders of German shepherds to donate siblings of dogs that died suddenly in their sleep, and she started tracing pedigrees. She deliberately bred dogs with the inherited predisposition for the abnormality. That concentrated the genes -- although the

researchers still don't know which genes are responsible -- and pedigree charts of inbred dogs with inherited arrhythmias began to look like family trees of old European royalty with hemophilia.

That's how a puppy named after a snow-capped mountain became Shasta Science Dog.

"Brian Maloney, one of the veterinarians at the clinic where Shasta was supposed to be spayed, had been an intern at Cornell, and he said he recognized the arrhythmias," Robyn Hoffman said. With the Hoffmans' permission, Shasta was fitted with a portable, 24-hour-a-day heart monitor. One day's reading was enough for Mo•se.

"Her ECG (electrocardiogram) was perfectly normal when she was awake and excited and happy," the Cornell veterinary researcher said. "When she went to sleep, the arrhythmias started. I knew this dog was going to die unless . . ." Cornell requested Shasta's participation in the SIDS-related research. The dog would be fitted with an implanted defibrillator to control her racing heart. And she would have puppies of her own. The Hoffmans thought long and hard, Robyn Hoffman said, and finally decided: "If there was some way our dog or her puppies could save a life, then we had an obligation."

Shasta was flown from San Francisco to Ithaca. Her defibrillator was implanted by James A. Flanders, D.V.M., with assistance from Eric Fain, M.D., a physician/computer specialist from Ventritex Inc., the Sunnydale, Calif., manufacturer of the complex device. With Fain's programming assistance, the defibrillator worked. Shasta became, from all outward appearances, a normal German shepherd: healthy, vigorous and fertile. And she was finally getting a good night's sleep.

Not so, though, for Mo•se and her assistants. They often spend their nights watching over newborn puppies to make sure not a single one is lost. Canine mothers, especially first- timers with large litters, may unknowingly roll over and crush the tiny pups, Mo•se said, and every animal in the Cornell project is precious. Some of Shasta's pups inherited the abnormality. In addition to the dangerous arrhythmias, the affected animals had abnormal sympathetic nerve innervation to the heart. Collaborating researchers at the University of California at San Francisco (UCSF) confirmed the Cornell veterinarians' hypothesis of uneven distribution of nerve fibers.

Drs. Michael Dae and Randall Lee produced images of the heart with MIBG (metaiodobenzylguanidine) scintigraphy that showed the incomplete nervous innervation. Dr. Phillip Ursell, also at UCSF, corroborated the paucity of nerves, using special stains of the hearts of dogs that died. The affected dogs' heart muscles -- which should be as full of nerves as Los Angeles is crammed with freeways -- look more like road maps of the Yukon.

Another important finding at Cornell was the discovery of abnormal electrical activity in individual heart fibers taken from dogs that had died. The relationship between abnormal electrical activity and lack of innervation is under study in collaboration with Robert F. Gilmour Jr., Ph.D., Cornell associate professor of physiology specializing in electrophysiology of cardiac tissue.

"Dogs are like people. Their nerves to the heart are not complete at birth," Mo•se explained. "But the nerves should continue growing to the heart during the weeks and months after birth. The sudden death dogs -- and even those that survive -- never seem to develop a normal nervous system. We're not sure whether this is a problem with the heart or with the development of the nervous system." Nor are German shepherds the model that parallels human SIDS, the veterinary cardiologist emphasized. SIDS is a catch-all term for many of the unexplained, unexpected infant deaths, she said, and how many deaths are heart-related is not clear.

"However, these dogs give us an opportunity to look at a couple of hypotheses, including the effect of abnormal innervation to the heart," Mo•se said, pointing to scintigraphy images.

Back in California, the Hoffmans were getting different pictures. Photographs of Shasta and her puppies, romping with veterinary students who exercise the dogs, arrived regularly in the mail. Mo•se and her colleagues began publishing their findings about German shepherd arrhythmias in journals for human cardiology, physiology and pediatric medicine.

They also reported to the animal care professions, asking veterinarians to be alert for the inherited abnormality and recommending that breeders keep known carriers out of the gene pool. One ultimate goal is to identify the genes responsible for the disorder, Mo•se said. Genetic screening could keep the sudden death problem from spreading through the dog population. And gene studies may help the investigation of sudden death in humans.

"But first we have to focus on the mechanisms of this disorder," Mo•se said, "and we still have a lot to learn." Shasta had been at Cornell about 18 months when something like a miracle occurred. Her sleeping arrhythmias simply stopped. The veterinarians checked again and again and it was true: Her 2-year-old heart was beating normally, asleep or awake, without aid of the defibrillator. The Cornell researchers now know that some of the arrhythmia-affected dogs "outgrow" the problem. Their normal autonomic nervous system still is not complete, but apparently they find other ways to adjust to this deficiency.

So Shasta Science Dog could go home.

Shasta "fit in" as if she'd never been gone, caring lovingly for the Hoffman kids (three by now) and running like a marathoner with Jake and the gang. Robyn Hoffman said she's never seen a dog so protective of children.

Before the Cornell veterinarians put Shasta on the plane to California, they gave her a little thank-you for her contributions to science. She finally got that long-awaited spaying procedure.