Electrolytes are substances -- like sodium and potassium -- that become ionic conductors when dissolved in fluid. They're beneficial because they assist cells in sending electrical impulses to other cells. Because you can lose electrolytes when you sweat heavily, replenishing them as soon as possible is critical. So, while electrolytes won't specifically reduce heat intolerance, they do address a side effect of it.
The easiest way to reintroduce electrolytes into your system is to drink a beverage formulated with them. Many sports drinks contain electrolytes, but they also tend to be high in sugar -- which can be a problem if you're diabetic or on a weight-loss plan. However, there are some -- particularly those formulated for children -- that have less sugar.
The supplement mentioned on the next page may help you with a widespread cause of heat intolerance.