From CNN Medical Correspondent Dan Rutz

(CNN) -- On admission, new hospital patients are often asked what they would want done if their hearts stop beating. About one in four congestive heart failure patients checked "do not resuscitate" in a survey of a thousand admittance records.

But nearly half later changed their minds, according to a study published by the American Heart Association.

"When people are in the hospital and doing poorly they may be more likely to be pessimistic about their overall outcome," said lead researcher Dr. Harlan Krumholz of Yale University.

Krumholz said congestive heart failure often takes a roller coaster course.

"[Patients] can have interludes in which they feel quite well ... punctuated by episodes in which they feel quite bad," he said.

Peter Gaspar suffers from another life-threatening condition. He said at one point in his illness, he wanted to die.

"A lot of things have happened," he said. "I found out that I still have a life."

While Gasper says he still wouldn't favor emergency resuscitation, in the years since overcoming depression, he no longer wants doctors to help end his life.

"I believe it's up to doctors to take an interest in their patients and in that interest to understand that their preferences on this very important issue can change," Krumholz said.

However, the most important find may be that in one out of four cases, doctors were unaware of their patients' attitudes about resuscitation.

Krumholz says the solution is frequent, open discussion, preferably before a crisis, to prevent misunderstandings.