Since December 1, 43 people suffering from heat-related illness had been admitted to ACT emergency departments.

Canberra Hospital's emergency department clinical director, Greg Hollis, said most cases were of sunburn and heat exhaustion.

"Particularly for the elderly, we've had presentations for heat-related illness, and also for young children as well, being another at risk group," he said.

"Where [the elderly] have been outside in the garden and become dehydrated and suffered quite significant injury related to elevated body temperature, as well as effects such as kidney failure, so there are some quite significant effects."

There was no significant spike in heat-related admissions while Summernats had been on.

Heat hospitalisations were a small percentage of the Canberra Hospital's roughly 200 daily presentations to the ED, however complications of heatstroke could be quite severe.

Working out what fluid to give a dehydrated patient and how rapidly could be difficult once they become critically ill, he said.

"So one of the biggest things is preventing it, so looking out for things like dry mouth and your eyes not tearing anymore, and if you actually stop sweating.

"Also muscle cramps, nausea and vomiting, palpitations and light-headedness."

He said by the time a body temperature has risen severely, the brain's and body's ability to react is affected, becoming a "vicious cycle" and causing quick deterioration.

Dr Hollis urges anyone experiencing even subtle dehydration symptoms to find shade immediately and drink frequent but small amounts of water as too much too quickly can trigger vomiting.

While keeping children's fluids up and checking that they are urinating regularly is important, keeping an eye on objects that can heat up is also crucial.

"There are the obvious things like getting in the car with seatbelts, but also other things in the environment that would normally be fine for them but that they might suffer direct injury from [in the heat]."

Pets will also need extra water and shade.

Find more detailed tips at www.health.act.gov.au