The accidental discovery last year of an aneurysm in my aortic artery was fortuitous. This is what doctors tell me, anyway, and I mostly believe it. Knowledge of the aneurysm means I can keep an eye on it and have it surgically removed before it reaches a size where rupture is a serious danger.

But knowledge of its existence also makes me hypersensitive to every twinge in my chest and leaves me constantly wondering: Am I about to die? This unending state of alert could wind up killing me. The biggest danger for anyone with an aortic aneurysm is high blood pressure -- and my blood pressure started climbing the instant I learned about this aneurysm.

Researchers have learned a lot in recent years about the role of various factors -- genes, gender, medication -- in the development of all sorts of illnesses. More people than ever know they're at higher risk for cancer, or heart disease, or diabetes. But what about the risk of knowledge?

Discovering that your largest artery contains a bulge that any moment could burst and kill you changes the way you think about yourself. News of my aneurysm slayed the self-perception I'd had -- that of a superhealthy 43-year-old triathlete. Suddenly, I was a Code Blue just waiting to happen. A view of one's self as unhealthy can become self-fulfilling, many doctors say.

Stark Evidence: This MRI image shows the author's aneurysm. The aorta is the lighter object shaped like a question mark. The aneurysm is the wider section of the aorta on the left side of the question mark.

In part, that's because knowledge can change behavior for the worse. Although this aneurysm means I should be even more careful about my health, it has had the opposite effect. I no longer impose upon myself a Draconian diet. I've stopped taking vitamins inexplicably, gained a little weight and resumed my old love affair with caffeine, which I'd given up years ago in an effort to keep down my blood pressure (which I now suppress with pills). I exercise more vigorously than some aneurysm specialists believe I should.

The point is, I'm now less bent on reaching old age than on enjoying my present age. As a friend of mine said upon hearing about the aneurysm: "If this can happen to you, we should all eat whatever we want."

The importance of knowledge as a factor in medical outcomes is large, growing -- and little understood. Advances in medical genetics, for instance, are enabling doctors to identify the genes that predispose us to certain cancers. Similarly, until the recent advent of CT and MRI scans, aortic aneurysms (which don't show up well on X-rays) remained undetected until they ruptured or dissected, which is an often-fatal tear in the inner lining of the arterial wall. But now, scores of scans taken to look for gallstones or coronary calcium are accidentally catching something more serious -- asymptomatic aortic aneurysms.

A Prophecy Fulfilled

In theory, such knowledge can enable us to act pre-emptively. But 2,500 years before the invention of the CT scan, Sophocles wrote about how such pre-emptive action can backfire. His drama Oedipus Rex illustrated vividly the danger of receiving knowledge of one's fate. Told by an oracle that he is doomed to slay his father and marry his mother, Oedipus flees the kingdom of his parents -- unaware that they adopted him. Arriving then in the land of his biological parents, Oedipus unintentionally fulfills the awful prophecy.

Like the oracle Oedipus received, CT scans of asymptomatic aneurysms in some cases have set in motion tragic chains of events. Some people, consumed by this perhaps fatal flaw near their heart, opt for serious surgery -- and die from the operation. They've, in effect, killed themselves by seeking to eliminate an aneurysm that might never have burst.

As someone whose aorta is about 1.5 centimeters too large to be normal and a centimeter short of the current surgical standard, I've come to accept that the only certainty about aneurysms is danger. You're in danger if you act. You're in danger if you don't.

So you begin by trying to forget about it. This is what my swimming pal does. He is a cardiac surgeon who happens to have an aortic aneurysm, and when I first learned about mine he was very reassuring. He shrugged it off, said he and I just have big aortas, that we'd monitor them and have surgery if they got bigger. No big deal. It gave me tremendous comfort to see that his aneurysm didn't worry him. Then one day at the pool he told me that a sudden swoon had sent him recently to the emergency room. "I thought I was dissecting," he said. It turned out to be nothing, but the episode had the disappointing effect of revealing my hero to be only human.

It also confirmed what I already knew: You can "forget about it" only so much. After learning about my aneurysm I started experiencing a sensation of tightness in the left side of my chest. I assumed this was psychosomatic, because I'd never noticed it before, and also because the physicians I consulted shrugged it off, saying this happened to everyone who got diagnosed with an asymptomatic aneurysm. But it was clear to me that they didn't really know whether an enlarged aorta might be painful, and it also occurred to me that swollen body parts are usually sore. Then I interviewed an aortic expert -- a chief of cardiovascular surgery at a top academic hospital -- who said he is convinced small aneurysms do cause pain. Now every sensation in my chest feels dangerous.

Dreaming of John Ritter

A few days after the death from aortic dissection last month of Hollywood star John Ritter, I had a dream that I was sharing a house with two women who were only my roommates. The dream puzzled me until I remembered that this was the role that John Ritter had played in his most famous sitcom, "Three's Company." Suddenly the dreadful meaning was clear: I had become John Ritter. Becoming John Ritter is now the fear of everyone with a known aortic aneurysm.

And so, I can't forget. The aneurysm won't let me. It is a constant reminder that I am going to die, preventing me from engaging in the daily denial of death that psychiatrists say shores us up. This is why some people demand surgery the instant their aneurysm is diagnosed, no matter how small it is, no matter how unlikely it is to kill them; they will do anything to allow them to deny death once again.

In my case I suspect that denial was stronger than average, because of the triathlons I completed. The allure of triathlons is the illusion you get of invincibility. Following the Sept. 11 terrorist attacks, I wasn't the only triathlete to gulp hard at the revelation that some extremely accomplished triathletes failed to escape the top floors of the Twin Towers, our irrational assumption being that completing an Ironman race prepares you for anything.

Yet that gulp was nothing compared with the news of my aneurysm. Last April when I wrote in these pages of the shock of learning about this condition (A Time Bomb Near My Heart), I received hundreds of sympathetic letters. But the one I remember best was from a reader who said, "I have bad news for you and all the other health nuts. One of these days you are going to die." That, it seems to me, is the message of my aneurysm, and there's no escaping it.

Betrayal and Freedom

But to live daily with the knowledge of death is not all bad.

It has shown me that some of what I did in the name of prevention was actually a form of cowardice, of not facing my mortality. I'd made a kind of unconscious pact that if I scored a perfect grade on those tests that ask how well you take care of yourself, I'd live a very long time. Then along came the aneurysm, and I felt betrayed -- and freed. With the pact broken, I no longer had to be perfect. And amid the constant threat of death, I no longer saw the point of it. Eating only "good fats" does indeed improve your chances against heart disease, but it guarantees you nothing. Avoiding butter is no discipline if what you're really avoiding is the truth. It's true that staying healthy and fit improves the quality of life regardless of longevity, but I believe I went too far: Prevention was a religion for me until the aneurysm put a spotlight on its substantial limitations.

In the past year I've been reminded of my childhood fascination with the Sioux, and specifically their cultural distaste for fear of death. When death was imminent, their custom wasn't to scream or run. They sang. Let's face it: To let fear of death rule you is cowardly. I can't escape death, but I can show it -- with a pat of butter or harder swim than is recommended for me now -- that it no longer has me running.