Cocaine can cause irregular heartbeats that lead to heart attacks and sudden death in young people with no history of health problems, a team of Tufts University doctors has found.

Reporting at a conference of the American Heart Association, Dr. Jeffrey M. Isner said it is unclear exactly how the drug caused the effects but that he and his colleagues have found seven cases in which people between the ages of 20 and 37 were hospitalized or died suddenly of heart disorders immediately after using large amounts of cocaine.

Two of the users died, one of a heart attack and the other of wildly irregular heartbeats. The others had disabling episodes of irregular heartbeats, called ventricular arrhythmias.

"The cardiac consequences of cocaine abuse have been vastly underestimated because most people have not been looking for it," Isner said. "But now that we have started to look for it, I'm sure it's going to be apparent that this phenomenon is widespread."

Isner said that many cases of cocaine-caused arrhythmias have probably gone undiagnosed because most patients deny using illegal drugs when questioned by doctors.

In other cases where young people have died of arrhythmias, Isner said death is often attributed to depression of the nervous respiratory systems.