The heart attack occurred last Friday, according to a statement from Winters' family.
"Over the past few days, she has become much stronger, and Shelley is nearly back to her normal self. We are so thankful to Shelley's fans for their support and words of encouragement," the family said.
Winters, 85, was being treated at an undisclosed hospital in the Los Angeles area and was expected to be released within a week, a spokesman for the family said Wednesday.
The actress, who played blonde bombshell roles in the 1940s and went on to excel at drama, won supporting-actress Oscars for her work in "The Diary of Anne Frank" (1959) and "A Patch of Blue" (1965). She was nominated for "A Place in the Sun" (1951) and "The Poseidon Adventure" (1972).