WASHINGTON -- Federal officials are investigating whether the smallpox vaccine contributed to the heart attack death of a Maryland woman and brought on heart problems in six others.

The vaccination has never been associated with heart problems before, but health officials are now recommending that people with a history of heart trouble refrain from being vaccinated while authorities investigate a possible link.

"It's a balance, and I think we want to err on the side of safety," Dr. Julie Gerberding, director of the Centers of Disease Control and Prevention, said Tuesday.

Three of the seven people under investigation suffered heart attacks, including the Maryland woman who died, another woman who is now on life support and a third woman who was hospitalized and released.

All three were health care or public health workers in their 50s.

Two other people developed angina, or chest pain.

All five of these patients had risk factors for heart disease before the vaccination, such as diabetes, obesity, hypertension or use of tobacco, Gerberding said.

The other two patients under investigation suffered from heart inflammation, which is not associated with those risk factors.

Gerberding said she does not expect to find a link between the heart trouble and the vaccine but wants further study before ruling it out.

Based on historic data, a small number of people who receive smallpox vaccinations will die and a few will develop life-threatening complications.

Those complications have never included heart problems, but the data were gathered during a time when most people being vaccinated were young children who were not likely to have heart trouble, Gerberding noted.

"We acknowledge that we don't have a lot of epidemiological or scientific information about the relationship between vaccine and cardiac illness in persons who are older," she said.

The CDC planned to gather cardiac experts on Wednesday to consider whether something in the vaccine might be triggering heart problems in people who already have risk factors.

Health officials also plan to compare the rate of heart problems in the pool of smallpox vaccine recipients with the rate expected in a similar population of people who have not been vaccinated.

Under the new temporary guidelines, people who have been diagnosed with serious heart disease such as coronary artery disease, congestive heart failure, heart attack and angina are being told not to get the vaccine. The change was ordered by Health and Human Services Secretary Tommy Thompson.

Gerberding emphasized that the program must move forward as the nation prepares for the possibility that smallpox could be used as a bioterror weapon. She said she does not expect the new guidelines to significantly affect the number who wind up being vaccinated.

"The potential for terrorism has probably never been higher," she said. "We must continue to be prepared."

The woman who died, a hospital worker in Salisbury, Md., was vaccinated a week ago. She died five days later, on Sunday, in Arlington, Va., according to Karen Black of the Maryland Department of Health and Mental Hygiene. An autopsy was performed Tuesday.

Her death is the first associated with either the civilian vaccination program that began two months ago or the military program launched in December.

As of March 14, states had vaccinated 21,698 civilians, mostly in public health departments and hospitals. Concerns about the vaccine's risk have helped keep the numbers well below the 450,000 initially expected.

The military program, where vaccinations are mandatory, has vaccinated "well over" 100,000 soldiers, the Pentagon said.

Based on studies in the late 1960s, experts estimate that one or two people out of every million being vaccinated for the first time will die. The death rate for those being revaccinated was lower: Two people died out of 8.5 million who were revaccinated in a 1968 study.

Additionally, 14 to 52 people out of every million being vaccinated for the first time are expected to suffer life-threatening side effects.

That's because the smallpox vaccine is made with a live virus called vaccinia, a cousin to smallpox which can cause illness if it escapes the inoculation site and infects another part of the body. Vaccinia can also infect those who touch someone else's vaccination site.

The question now, Gerberding said, is whether the viral infection caused by the vaccine is somehow exacerbating pre-existing heart conditions.

The last U.S. case of smallpox was in 1949, and routine vaccinations against the disease ended here in 1972, as the disease was on the wane globally.

In December, President Bush ordered that vaccinations resume for health workers, emergency responders and the military amid fears that smallpox could be used as a bioterror weapon.