Without the Mazda heater hoses functioning as expected, the passenger compartment will be a cold place to be in the winter time. There are two heater hoses on your Mazda that are the conduits for the heated coolant to travel from the engine to the heater core, and then ultimately to the defroster or the passenger compartment.
The Mazda heater hose that generally fails is the supply line from the engine to the heater core. This is the polymer conduit that his exposed to the highest level of heat. It is the heat that helps to accelerate the deterioration of the polymer of which the hose is constructed.
The heater hose will wear out in a similar fashion to how a coolant hose would; as more and more hot coolant passes through the hoses, the polymer will expand and become thinner due to heat related breakdown. The most common place for this to occur is where the heater hose is connected to the Mazda engine block because this is the place on the hose that is exposed to the highest level of heat on a constant basis.
It is the thinning of the walls of the heater hose that causes a leak to occur eventually. If the Mazda owner does a regular weekly inspection of the components under the hood, the leak can be avoided by noticing this condition on the hose before it becomes a problem. This way, any other issue pertaining to the engine, its accessories, and components like the coolant and heater system can be averted. If a regular inspection is not done on a constant basis, a hose or belt failure can occur without warning.