Heat cramps are painful, involuntary muscle spasms that typically occur during heavy exercise in hot environments. You're most likely to get heat cramps in the calf, arm, abdomen and back. Next time you experience heat cramps, here's what to do: 1. Rest briefly and cool down. 2. Drink clear juice or an electrolyte-containing sports drink. 3. Gently stretch and massage the affected muscles. 4. Call your doctor if the cramps don't go away in an hour.