Extreme heat is settling over Indianapolis, and doctors say heat illness can move quickly from muscle cramps to a life-threatening emergency.Prevention starts with water, shade, and knowing when to get help, said Dr. Robert Bier nbaum, chief medical officer at WellNow Urgent Care.3 stages of heat illnessBiernbaum said the key is knowing which warning signs you can treat and which ones require a 911 call.The first is heat cramps. Its the mildest form. People experience involuntary muscle spasms normally in their calves, thighs, and abdomen. However, their core temperature is normal, Biernbaum said.The next one is heat exhaustion. This means your body is really, really struggling to cool itself. People have the same type of muscle spasms, but also are dizzy, weak, nauseous, and really, really sweating heavily, he said.The final phase is heat stroke. That is when the bodys ability to cool itself down has completely failed. You have to call 911 immediately.Biernbaum said his clinics see heat-related illness regularly in the summer. Heat cramps and heat exhaustion can often be treated at urgent care, but heat stroke is different.Prevention matters mostStaying ahead of the heat matters more than treating it after it starts, Biernbaum said.The most important thing though for heat related illness is prevention, he said. Always keep yourself hydrated constantly drink water in hot temperatures, make sure that youre wearing light and loose fitting clothing, and get out of the sun. When youre out there for a long period of time, make sure to get in the shade, cool yourself down, take breaks, drink water. When your body starts getting cramps, that is a signal its time to move out of the sun and cool yourself down.When to call 911If symptoms get worse or confusion sets in, doctors say that is the moment to call 911.How to stay safe in extreme heat Drink water constantly, dont wait until thirsty Wear light, loose-fitting clothing Take frequent shade breaks Move out of sun at first sign of cramps Check on elderly neighbors, kids, and pets Call 911 for confusion, loss of consciousness, or no sweating ...read more read less