The caution is especially alarming as the pandemic is predicted to surge this autumn.o reduce the risks, doctors are advising heart patients to take the H1N1 vaccine as soon as it becomes available in Oct 2009.
Nearly 2.5 million people with cardio-vascular complications and asthma and diabetes patients are expected to be given the vaccine.
Andrew Hayward, an epidemiologist at University College London, and colleagues at the London School of Hygiene and Tropical Medicine, checked 39 studies conducted between 1932 and 2008 and concluded that heart patients formed about 35 to 50 percent of increased flu deaths.
They have called upon these patients to get the vaccine dose as soon as possible.
Times Online quoted the scientists as writing, "During influenza epidemics there are many deaths and serious complications in vulnerable populations.
People with underlying chronic medical disorders such as cardiovascular disease are particularly at risk ... We believe influenza vaccination should be encouraged - especially in those people with existing cardiovascular disease."