I got into cycling in the mid 80s in Texas at about the same time and same locations that Lance Armstrong dropped out of football and began tearing things up in road races in north central Texas.
I commuted -- by bike -- 20 miles every day from the north side of Fort Worth to my job in Irving, crossing through North Richland Hills, across the Mid Cities of Hurst/Bedford/Euless, through DFW Airport and to my job on Valley View Lane in Irving.
Texas residents know that Texas can get and stay hot through the summer time. I'd arrive home covered with white salt -- the leavings of my evaporated sweat. But I didn't have a hard time with the heat because I was acclimated to the heat.
I live near Santa Cruz, California now, inland from the beach about five miles and 600 feet higher. I am not heat acclimated now. Because of my past experience, however, I didn't think riding around in the heat would bother me. It did.
I cycled downhill the Santa Cruz, went west a ways to Capitola and Aptos, circled back to Santa Cruz, then took Graham Hill Road up straight up to Felton. Up in elevation and in temperature.
Foolish me, I only had one water bottle with me. I kept it full by stopping at gas stations for water and gatorade. It's only six miles to Felton while I climbed to an elevation of over 700 feet before dropping back down into Felton. In the meantime, the temperature soared from 87 degrees to 110 degrees in Felton. I ran out of water at three miles but I was still feeling good, pushing myself at 15 mph on the uphill grade. At four miles I started feeling a little weak and slowed down to 11 mph. When I finally reached Felton I was dying, coasting on the downhills and barely staying a 7 to 11 mph on the uphills segments. I stopped at Safeway and bought a liter of water and a liter of PowerAde and sucked about half of it down right away.
I still had another five miles of mostly uphill to go for home. After a short rest I thought I felt better, but as soon as I hit the hot sun the weakness set in again, along with some nausea. I removed the foam insulation from my head and pressed on the mostly uphill ride home at 5 to 7 mph.
I got home, obviously, and took a nice cool shower. Then I jumped into the pool. Important tip: NEVER jump into a cold swimming pool after exerting yourself in the heat. Doing so may will result in very painful leg cramps.
After that, I slept a full twelve hours. My dog woke me up begging to be let out for a walk.
Ah Santa Cruz. That's where I bought my beater bike. I was there for the summer and the ocean-cooling effect made for glorious riding weather. I hadn't yet gotten hooked on cycling, and I remember one day just wanting to bike down the Pacific Coast as far as I could go. I think I only made it as far as sunset state beach but to my novice biker self it seemed like a fun adventure.