(FORTUNE Magazine) – To judge from the recent flurry of stories linking the impotence drug Viagra to heart attacks, you'd think some dark agent of death had come among us. But it's actually surprising that more Viagra-associated deaths haven't been reported.

If you tracked a million U.S. men ages 45 and older for a month, more than 700 would be expected to die from heart disease, according to federal statistics. Given that since its April launch Viagra has been prescribed to 1.7 million men--most of them over 50--it's hardly shocking that as of press time, 16 deaths had been reported among them. Indeed, 13 of those men had histories of cardiovascular disease or showed heart-attack symptoms, according to the Food and Drug Administration. And in half the cases it was unclear whether the men had even taken Viagra near the time of death.

It's certainly possible that the number of fatalities among Viagra patients will rise considerably. But intense coverage of the issue should have scared up more reports of deaths by now if a truly alarming number had occurred. So far, the FDA and impotence experts see little cause for worry.

Besides, doctors have been telling us for some time that impotent men are at elevated risk of heart attacks. Small arteries that fill the penis with blood to produce erections tend to get clogged with fatty deposits before big coronary vessels do, so impotence often signals heart disease. (FORTUNE covered this issue months ago in "The Selling of Impotence," March 16; see story in the fortune.com archive.)

And lest we forget, sex can kill all by itself: For a healthy 50-year-old man, intercourse poses a heart-attack risk of about two in a million, says James Muller, director of the University of Kentucky's Gill Heart Institute. For sedentary men, whose lifestyles can contribute to impotence, the risk is much higher. So it's no great puzzle that some men on Viagra suffer heart attacks during or soon after sex, as was apparently the case in seven of the 16 Viagra-linked deaths.

Nor are the heart risks of impotent men limited to Viagra. Other erection- boosters--including Pharmacia & Upjohn's Caverject, an artery-dilating drug injected into the penis, and Vivus's MUSE, a pellet inserted into the urethra--can also tempt the weak of heart into overdoing it. FDA data show Caverject was linked to three deaths during its first eight months on the market, when only about 100,000 prescriptions were dispensed, according to market researcher IMS Health. That's triple the deaths per prescription reported for Viagra so far. Alarmists might conclude Caverject is quite risky, but again, statistically speaking, that would be ludicrous. As the FDA stresses, deaths associated with a drug aren't necessarily caused by it.

The FDA, however, has warned both Vivus and Pharmacia & Upjohn about failing to clearly convey the risks of their impotence drugs in promotional literature. Vivus's MUSE causes sudden blood-pressure drops in about 3% of men who take it; some even faint. Caverject's risks include busted needles (some men have broken off the needle in their penis) and abnormally long-lasting erections, which can damage tissues. The companies say they've addressed the FDA's concerns.

So far, Pfizer has been very forthcoming about Viagra's risks, and it recently reiterated them in a letter to every U.S. doctor. (Note: Viagra shouldn't be taken by heart patients using "nitrate" drugs for chest pain--the mix can cause dangerously low blood pressure.) Such warnings aren't likely to take the spotlight off future Viagra-linked deaths, but they do establish where responsibility lies: You can't say they didn't warn us.

--David Stipp