Depression doubles the risk of dying after a heart bypass, researchers have found.
The patients all had heart bypass operations
The scientists from Duke University Medical Center in North Carolina, say treating depression in this group of patients could cut deaths.
They suggest patients should be screened before surgery to assess their chances of developing depression.
But they call for more research into how depression increases the risk of dying.
Researchers examined 817 patients who were having bypass surgery between 1989 and 2001.
They were assessed for depression just before surgery, six months after surgery and then monitored regularly for an average of five years, though some were followed for as long as 12 years.
There were 122 deaths over five years.
Around 40% of patients were assessed as suffering depression.
Those found to have moderate to severe depression at the time of surgery or mild depression then and at the six-month assessment were more than twice as likely to die than patients who were not depressed.
Dr James Blumenthal, from the department of psychiatry at Duke University who led the study, said: "We believe that psychological assessment before and after surgery could be a low-cost and relatively easy way of potentially saving lives."
He added: "Despite advances in the medical management of patients after CABG, the prognostic importance of clinical depression provides a further opportunity to reduce adverse outcomes associated with the procedure by treating depressed patients after surgery.
"We observed that, after adjustment for other risk factors, depression was associated with a two-to-three-fold increase in risk.
"Thus, many patients who undergo CABG are at increased risk of death because they are clinically depressed; this risk could be reduced by treatment of depression after surgery."
He added: "Future studies should investigate the mechanisms responsible for this increased risk and whether treating depression can reduce the risk of death in depressed patients undergoing CABG."
Depression has been linked to other risk factors for cardiovascular disease such as smoking, high blood pressure and obesity.
The Duke University researchers are now carrying out further research to look at potential mechanisms for how depression may increase the risk of death in heart bypass patients.
The research is published in The Lancet.