Try to beat the heat. Run as early as possible without sacrificing your sleep and recovery. If you can't do mornings, try and do it when the sun goes down. Go slow, slower than you might think. Summer is for building the base for the fall workouts, so keep the effort low on most of your mileage, key is to get time on feet in while staying healthy. Heart rate will naturally be higher when first building back from off time as well as with the temperature being up. It will come down as you get fitter. I'm also a fan of doubles if you can do them, even at lower mileage, as you still get time in without the strain of longer easy runs that can fatigue you early on. For me, it helped build me up until I was aerobically fit enough to run longer.