in this gallery Summer is holding a metal heart. i am wondering if it is a tin man/Terminator reference? tin man from the Wizard of Oz. as in Terminators have no heart.
That's what I thought as well, but I remember reading that it was just a cooincidence, the heart symbol thing was part of Channel 9's promo ("I love Channel 9" or some similar slogan) for the TV shows they were featuring.
Cameron does have a heart, it just happens to be a shielded nuclear power source (she "bared her heart" to John in the bed scene towards the end of "Born to Run")