On a crisp, sunny July morning in San Francisco, my good friend and jogging buddy Bill Goggins began his push to post a 3-hour marathon. I'd decided not to join him; Bill always ran too fast for me. On any given jog, he'd invariably say, "How about we pick it up a bit?" It took me a year to develop the mental fortitude to resist.

The day before the race, I met Bill for lunch. He looked great, and he was clearly happy. The next morning, he got off to a good start. For the first 7.5 miles, he averaged a little over 7 minutes a mile. Runners generally slow as they tire. Not Bill. At the halfway mark, he sped up. And then, at the marathon's 24th mile, Bill smiled for the cameras and, mid-stride, dropped dead.

It was inconceivable. Bill was 43 years old and, by all accounts, in the best shape of his life. For as long as I'd known him, he'd stay out late drinking Fernet Branca, a bitter Italian liquor, and still meet me at 7 the next morning looking fresh and indomitable. He'd run a step ahead of me, glancing over his shoulder to tell me stories about the people he'd laughed with through the night. And though I had surely been asleep while he was having these grand adventures, I still couldn't keep up.

During the 6 months after Bill's death, I felt numb. But slowly, my denial morphed into a series of questions. Today I'm left with just one: Why?

***

In December 2005, 8 months before Bill died, he and I went for an early-morning run along the Embarcadero, the walk way beside San Francisco Bay. The air smelled of salt water and creosote from the wharf pilings. Sixty years ago, the area would have been crowded with longshoremen and ships from around the world. Today it's dotted with joggers in fleece jackets and leggings.

Back in 1951, an enterprising University of California at Berkeley doctor initiated a study of the men working these wharves. The researcher, Ralph S. Paffenbarger Jr., M.D., wanted to know whether cargo handlers, who performed strenuous physical labor all day, had different rates of heart disease than men with more-sedentary jobs had. He did an initial exam and then, 18 years later, checked them all again. He discovered that the less-active workers had a 27 percent higher death rate than the cargo handlers did. In a seminal 1986 report that laid the groundwork for the exercise boom that followed, Dr. Paffenbarger concluded that physical exercise prolongs life.

This year, that assertion quietly received an asterisk. In April, the American Heart Association released a scientific statement noting that although regular physical exercise is now widely advocated by the medical community, studies show it can increase your risk of early death. A study published in the Journal of the American Medical Association found that joggers in Rhode Island were 7.6 times more likely to die early than people who didn't run. In another study, published in the New England Journal of Medicine, researchers reported that the incidence of cardiac arrest during exercise was 25 times higher than during light activity or while resting. The AHA statement concluded that exercise "acutely" increases the risk of sudden death in "susceptible persons." For these people, "the health risks of vigorous physical activity almost certainly exceed the benefits."

Susceptible persons . . . was Bill one of them? Did he suffer from something he had no knowledge of? The only way to find out was to dig up his autopsy report, so, with consent from Bill's family, I called the San Francisco medical examiner's office and requested a copy of their findings. The following Tuesday, a little after 9 in the morning, a man with a skull tattooed on his forearm slid me a white envelope marked with both my name and Bill's, as if our collective fate was sealed within.

I returned to my car and began reading. The case history was concise: "The subject, Mr. William Goggins, a 43-year-old male, collapsed while running in the San Francisco Marathon and was transported to [San Francisco General Hospital], where he expired." The autopsy findings came a couple of pages later: "Cause of Death Due To: Hypertrophic Cardiomyopathy."

Hypertrophic cardio-what?

***

"If your friend hadn't run that marathon, there's a good chance he could have lived a long life," says Lisa Salberg, president of the Hypertrophic Cardiomyopathy Association. I've called her looking for answers. She asks me to read Bill's autopsy findings to her, and when I reach the section about the thickness of the wall separating the chambers of his heart—1.7 centimeters—she stops me.

"Anything more than 1.5 centimeters is definitive," says Salberg. She explains that HCM is characterized by the thickening of heart muscle. As the muscle wall separating the right and left ventricles bulges, it obstructs the flow of oxygenated blood leaving the heart through the aorta, making it more difficult for the heart to function, particularly during exercise. It's caused by a genetic flaw that can be passed down from either parent. So far, researchers have pinpointed 14 genes associated with the condition. Those who carry any one of these genes generally develop HCM during adolescence or early adulthood.

Then she drops a whopper: One in 500 people has HCM. It's more prevalent in the United States than is HIV and Parkinson's.

And then another whopper: You know you have HCM if you die unexpectedly. That's often the first symptom. About 15 people in this country drop dead from the condition each day. It's the most common heart-related killer of men younger than 30.

"It steals people away in the prime of life who have no outward signs of illness," says Salberg. "They often just collapse without warning." At least 600,000 Americans, in other words, are walking around with a potentially deadly condition they're probably unaware of. Their chances of dying from HCM in any given year is about 1 percent, but the risk rises as they age. If you suffer from HCM, chances are it'll eventually kill you.

Salberg has HCM, as do her father and daughter. She formed the Hypertrophic Cardiomyopathy Association after her sister died of the disease in 1995. But without that kind of tragedy in a family, the disease can be hard to pinpoint. It sometimes produces heart palpitations, but these are often misdiagnosed as anxiety or panic attacks.

Salberg points me to medical journals like the Journal of the American College of Cardiology and the European Heart Journal. I stay up late reading research papers, and at around 3 a.m. it hits me. All the answers are here, hidden in plain view beneath such phrases as "morphologic protocol" and "phenotypic profile." Many athletes who died on the court or field—Hank Gathers, the Loyola Marymount basketball star; Thomas Herrion of the San Francisco 49ers; Reggie Lewis of the Boston Celtics—had HCM and probably didn't know it. That list now includes my friend Bill.

I can't help but wonder, Could these deaths have been prevented?

***

On February 18, 1982, the Italian Ministry of Health issued a decree. Henceforth, every athlete wishing to participate in a competitive sport would have to undergo cardiac screening. The testing would begin with a simple electrocardiogram, known as an ECG (or EKG), which would measure the electrical activity of the heart. If this test found abnormalities, doctors would order an echocardiogram, an ultrasound of the heart.

The athletes would pay for the annual test, but the government subsidized prices. The decree spawned a new industry for doctors, who pored over millions of cardiograms searching for HCM-afflicted hearts. If they found one, the athlete was prohibited from participating in vigorous competitive sports. His or her athletic options were abruptly reduced to golf and bocce.

Over the next 22 years, researchers scrutinized the data streaming in from the Italian screenings. The most comprehensive study focused on the region surrounding Venice, where sudden cardiovascular deaths in athletes between the ages of 12 and 35 plummeted by nearly 90 percent. Extrapolating those results, the researchers estimate that over the past 25 years, thousands of lives have been saved across Italy.

The Veneto report, published in 2006, has triggered a debate in the Western world. On one side are Italian cardiologists, who say that because comprehensive testing works in Italy, it could work elsewhere. On the other are American and British specialists, who are mostly dismissive.

"It would be impossible to accurately screen tens of thousands of runners for one of the big British or American marathons," says cardiologist Dan Tunstall Pedoe, FRCP, who was the medical director of the London Marathon for 26 years. "We don't have enough cardiologists to read all those ECGs and echocardiograms." Three times as many athletes compete in the New York and London marathons than in the Rome marathon, and though not every athlete would necessarily need to be screened before each race, many would likely schedule their yearly screening around such an event.

Equally challenging would be annual checkups for the millions of Americans who play locally just for kicks, including the 7.2 million young adults competing on high-school teams. Italy, by contrast, has only 2.9 million young adults of high-school age. "We just don't have the manpower to create a national program," says Barry Maron, M.D., director of the Hypertrophic Cardiomyopathy Center at the Minneapolis Heart Institute Foundation.

Pedoe points out another issue: ECGs often indicate a problem when there isn't one. Euan Ashley, MRCP, director of Stanford's Hypertrophic Cardiomyopathy Center, estimates that, because of their intense training, more than half of all athletes have abnormal ECGs. The result: A large number of athletes without HCM would be sent for an expensive echocardiogram. Italy's national health-care system helps defray costs there, but athletes in the United States would have to pony up thousands of dollars. Some kids wouldn't be able to afford to pay—or play.

The AHA, while acknowledging that exercise can kill, issued two statements in the spring reiterating its decade-old recommendation that U.S. health-care professionals screen for HCM using a good old stethoscope, along with a questionnaire that asks athletes to report any family history of heart trouble. But a stethoscope can identify only certain forms of HCM, the types in which the heart muscle is so thick that it produces an audible murmur. More often than not, there is no murmur. And the questionnaire is only as effective as the respondent wants it to be. Kids trying to make a team are unlikely to disqualify themselves.

"Medical history and physical-exam screening in the United States can certainly be improved," admits Dr. Maron, who served as chairman of the AHA scientific committee that issued the recommendation.

Pedoe worries that because testing would add cost and hassle, people might be dissuaded altogether from participating in sports. "For the vast majority of people, running a marathon is beneficial," he says. "For every person who dies, thousands of others are postponing or preventing their heart disease by exercising. Labeling a generally safe activity as more dangerous than it really is could do more harm than good."

In other words, Bill was collateral damage in society's effort to become healthier. I can't accept that my friend was sacrificed so the rest of us would stay motivated to exercise. And I'm sure the hundreds of thousands of Americans who have HCM would have a problem with their doctors viewing them as sacrificial lambs. If the Italians have found a way to prevent HCM deaths, why can't we?

I call the University of Padua, in Italy, and track down Gaetano Thiene, one of the doctors who conducted the Veneto study. I tell him Bill's story. "In the United States, the burden is on the athlete, and this is totally wrong," he tells me. "Life comes first.

"If your friend had lived in Italy," he says, "he would most likely still be alive today."

So the question is, how many people like Bill will we lose before we decide we've lost too many?

***

When I was 21, I ran the Napa Valley Marathon. At mile 20, I hit the wall and could barely move my legs for the last few miles. Afterward, I felt nauseated and couldn't stand. For the next week, I could barely climb stairs.

I hadn't thought of that experience for years—until Bill died. Nor had I ever worried about the mild chest pains I occasionally felt, until Salberg told me they're a common warning sign of HCM.

If the Napa Marathon had prescreened me, would they have found an abnormal heart? I schedule an ECG with my doctor and, a few days later, go in for the 10-minute test. A nurse tapes 12 sensors to my arms, legs, and chest. The wires running from the sensors snake into a small box, which spits out a heart-rate graph. To my alarm, the top of the graph is labeled with these words: Abnormal ECG.

ECGs sense suspicious electrical activity, but they don't provide a definitive picture. To really gauge my risk, I need an echocardiogram. So, 5 days later, I visit the Mayo Clinic in Minnesota, home to one of the country's oldest HCM centers. Since 1989, an entire team has been devoted to detecting and treating the illness. They see hundreds of patients a year.

After a nurse jams a small black probe into my ribs, the monitor to my right flutters and, suddenly, a curious image appears out of the static. An assembly line gone mad. Clouds of red hurtle across the screen, controlled by doors that frantically open and shut. The doors look overworked, as if they're constantly behind schedule. This bleak picture is my heart.

An hour later, I review the images with Steve Ommen, M.D., the fresh-faced head of the HCM Clinic. "Your right ventricle looks pretty large," he says. He uses a mouse to measure the chamber, to confirm his suspicion. "Yes, it's big."

Diagnosing athletes with HCM is complicated by the fact that hearts can grow naturally as a result of exercise. One of Dr. Ommen's patients is a basketball player whose heart is enlarged, its chamber walls thick. It's a result of either HCM or vigorous exercise—Dr. Ommen can't tell which. He asked the man to stop all forms of exercise for 3 months. If the enlargement is natural, the heart will shrink. Otherwise it's HCM, and the jock will have to give up hoops or risk dying every time he steps on a court.

Dr. Ommen's story makes me wonder what Bill would have done. Being a runner was part of who he was. If someone had advised him not to run, I think he might have said, "I'll take the risk."

"It's a difficult balance," Dr. Ommen tells me. "On the one hand, there are health risks associated with sitting around. On the other, exercising too hard can kill you. It's a tough question to answer."

It's also a controversial one. After the 2000 Olympics, the Italian swimmer and two-time gold medalist Domenico Fioravanti was diagnosed with HCM. In keeping with Italian regulations, Fioravanti was barred from further competitions. Fioravanti argued that competing should be his choice.

Dr. Ommen leans toward the monitor displaying my heart. If he tells me I have HCM, how will my life change? Will I stop running, and start thinking twice about rushing to catch a bus? Or will I choose, as some HCM patients do, to have a defibrillator installed in my chest, and then go about my daily life until, one day, my heart spasms and the defibrillator engages? "They say it feels like being struck by lightning and punched in the chest at the same time," Dr. Ommen says. When you recover your wits, you realize you should have died just then.

There are other treatment options as well. Drugs can improve bloodflow within the heart, but studies show they're effective in only two-thirds of patients. Surgeons can also try to cut out the thickened sections of heart muscle. It's a major surgery, fraught with risk, and it doesn't always work. But in one study, 70 percent of patients reported major improvements in their quality of life afterward.

Still, the best defense is knowledge. Athletes are the most-visible victims, but many more nonathletes die of HCM each year. Every member of a family that has experienced a perplexing heart-related death should be tested. For those who have HCM, altering their lifestyles is critical. Will that be me?

Dr. Ommen pulls up a different image of my heart and measures the thickness of the walls separating my left and right ventricles. "You're fine," he says.

At Bill's unofficial wake a few days after he died, I got drunk on Fernet, his favorite drink. I ended up in a parking garage in downtown San Francisco, hurling traffic cones off the third level. "He shouldn't have died," I shouted.

Now, a year later, I know I was right.

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