The accident occurred about 3:45 p.m. in the 7600 block of East Summit Trail, which is in the Las Sendas area of northeast Mesa, police said.
The child was in the driveway of the home when Heap moved a truck forward, striking her, police said.
She was taken to a local hospital, where she was pronounced dead, police said.
Heap was born in Mesa and attended Mountain View High School, where he starred in football before attending Arizona State University, where he was a two-time All-Pac-10 selection. After being selected as a first round pick in 2001, he played professionally for the Baltimore Ravens and Arizona Cardinals until announcing his retirement in 2012.