Your coolant is either low or leaking (cabin heat comes from blowing air across hot antifreeze in the heater core). Worst case scenario, your head gasket is blown. If your car isn’t running poorly, it may still be cracked or leaking into the head or down the side of the block. Best case, you just need to top off your coolant. So, step one, check your coolant level. Fill it up and pay attention to it for the next few days. If it starts disappearing, check for a sweet smell (very similar to pancakes, actually) from your exhaust. That smell and/or thick white smoke indicates that you’re burning coolant in the cylinders, which means your head gasket is toast. If that’s the case, stop driving to avoid any further damage to the head and have it checked by a mechanic. If it overheats too much or too often, the head can warp and resurfacing is really expensive, let alone the labor involved in removing and reinstalling it.