Federal health officials said last night that they are investigating whether a Maryland hospital worker's fatal heart attack was related to the smallpox inoculation she received this month.

Authorities also are investigating a second case in which a recently vaccinated woman, from an unidentified location, suffered a heart attack. She is on life support.

In total, seven people immunized in the two months the program has been underway have experienced cardiac-related complications, a development that so surprised officials that they have decided to screen out anyone diagnosed with heart conditions, Julie Gerberding, director of the Centers for Disease Control and Prevention, announced last night.

The unidentified Maryland woman was a nurse at Peninsula Regional Medical Center in Salisbury who had volunteered to be vaccinated, according to the hospital's chief executive, R. Alan Newberry. She died Sunday in Arlington, where she was attending a conference.

Historically, the smallpox vaccine has not been associated with heart failure, and in an emergency call with reporters, Gerberding emphasized that most of the seven appeared to have some history of heart problems.

"Coronary artery disease is a very common condition," she said. "We will certainly do everything we can to get to the bottom of this issue."

Federal officials are struggling to rejuvenate a vaccination program that was supposed to be a central element of the safeguards against bioterrorism.

Only 21,698 medical workers nationwide have responded to President Bush's December call for 500,000 volunteers to be inoculated against smallpox.

Many doctors and nurses have refused to participate, saying the risk of the vaccine outweighs the threat of a smallpox attack. The vaccine, made from live virus, has been known to cause severe, sometimes fatal, reactions in a small percentage of people inoculated.

For every 1 million people inoculated in the past, one or two people died, and as many as 52 suffered severe complications. More common side effects include rash, fever, malaise and, in some instances, blindness and encephalitis.

Some unions, hospitals and health departments have advised against immunization until Congress and the Bush administration agree on a compensation program for people who die or suffer severe complications from the vaccine.

Maryland health officials said the woman who died, who was married and in her fifties, was inoculated March 18 and showed no signs of distress. Arlington County health officials performed an autopsy.

"There is nothing that suggests at this point anything other than a normal death," said Arlington Health Director Susan Allan.

Maryland's health secretary, Nelson J. Sabatini, said there is no known connection between the woman's vaccination and her death.

"I feel terrible that a health care worker has died," Sabatini said. "My sympathy goes out to the family. Right now there is no reason to believe there is any causal relationship between the smallpox immunization and her death."

As of March 14, Maryland had immunized 317 people, Virginia 358 and the District four, according to the CDC. Nationwide, about 20 people have reported some type of complication from the vaccine.

The mysterious pattern of heart problems prompted the CDC to confer with a host of outside experts, including cardiologists and the Pentagon physicians who have inoculated hundreds of thousands of military personnel. One person in the military has suffered a heart-related problem since being vaccinated.

Gerberding said the administration has no intention of halting the program.

"This is still critically important to our preparedness capacity," she said. "The potential for terrorism has probably never been higher."

Staff writer Spencer S. Hsu contributed to this report.