Doctors attending a European cardiology meeting in Spain are concerned about the effects of a swine flu epidemic on patients with heart disease.
Some experts say heart patients should be among the first to receive a vaccine against the H1N1 virus.
Many heart failure patients experience a buildup of fluid in the lungs because there isn't enough blood being pumped efficiently. And drugs that are prescribed to deal with the problem aren't as effective if a patient catches the flu.
Doctors attending the conference in Barcelona say one bright spot is that most heart patients are 60 and older, which is the one age group that appears to be less susceptible to swine flu.
But a Swedish professor says catching swine flu "might be the last thing that pushes them over the edge."
In its recent guidelines, the World Health Organization named heart patients, HIV patients and pregnant women as the "at-risk" groups that should get the drug Tamiflu as soon as they are suspected of catching swine flu.