In their first interview since Brittany Murphy’s death last month, the mother and husband of the late actress tell People magazine that they believe she died from a congenital heart murmur, not drugs as has been rumored.

“She had a little bit of a cold,” says Murphy’s mother, Sharon. “You could never in a billion years imagine this happening.” The 32-year-old actress’ mother and husband, Simon Monjack, add that Murphy did not suffer from mental illness, an eating disorder, or a drug habit. “Do you not think anybody would have picked up on this anorexic, mentally deranged person?” asks Monjack. “It’s ludicrous.” Both say that Murphy’s heart condition was diagnosed in her teens and had been monitored regularly. “We had it checked out every which way you could imagine,” says Monjack.

Murphy’s mother adds that her daughter’s “bubbly” may have sparked the rumors of her drug use. “She never even drank. Maybe a glass of champagne at New Years,” says Sharon. “But everyone used to say she was wasted, she was this, she was that. It was hard for anyone to imagine that somebody was so high on life.”

The issue of People with the entire story will be on sale Jan. 22.