Did kitten have heatstroke.

the other day i tried to rescue a stray kitten who was suffering from heat stroke, but unfortunately it died. what could i have done better -- if anything?

when i first saw it, it was dragging itself across a sun beaten sidewalk (no shade in sight of where it was). i picked it up and tried to give it some water. it tried to drink, but not much luck there. i then got it into my air conditioned car to take it to a vet's office (which was less than a 10-minute drive). in the coolness of the car, it seemed to get a little better as it started moving more and fighting to get out my grasp (it was feral, remember). but then it seemed to have some sort of seizure. in the few minutes it took to get to the vet's office, it had gone limp, and i suspect died (or very close to it). the vet took it to the back exam room and in the course of me washing my hands, she came out and told me that the kitten didn't make it.

nyc is going through a bit of heat wave, and in case i ever see this again, what, if anything could i have done better? even though i did the best i could under the circumstances, and the odds are nothing could have been done as i don't know how long the kitten was out in the full sun and heat, i'm a little haunted, wondering if i could have done more.