(CNN) A Purple Heart recipient who fought in the Vietnam War sacrificed his life to save his 3-year-old granddaughter after the Oklahoma home they were in exploded, his son said.

Don Osteen, 69, died from from a heart attack during surgery on Monday after spending days fighting for his life, his son, Brendon Osteen, told CNN.

Brendon said his father was an Army veteran and was disabled in a grenade explosion during his service in Vietnam. "He was an old man who shouldn't have been able to do what he did," said Brendon Osteen.

Osteen's 3-year-old granddaughter, Paetyn, was also severely injured, with 30% of her body covered in burns, according to Brendon, who is Paetyn's father.

The explosion ripped through Osteen's house in Maud, about 58 miles southeast of Oklahoma City, September 19 . Brendon said his dad was lighting a candle next to a stove when there was a powerful propane gas explosion.

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