A PA-44 FLT INSTRUCTOR AND HIS STUDENT SHOWED SYMPTOMS OF CO POISONING AND HYPOXIA; APPARENTLY FROM A DEFECTIVE AIRCRAFT HEATER.

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WHILE WORKING IN THE PRACTICE AREA WITH MY STUDENT; I NOTICED MY VISION OF THE GLASS COCKPIT GETTING SLIGHTLY FUZZY. AFTER THIS STARTED; I ALSO NOTICED I WAS GETTING A SLIGHT HEADACHE. I BLAMED THIS ON THE FACT THAT I HAD BEEN WEARING MY CONTACTS ALL DAY AND THEY'VE BEEN KNOWN TO DO THIS; BUT I ALSO STARTED TO WATCH MYSELF FOR ANY FURTHER SYMPTOMS OF HYPOXIA/CARBON MONOXIDE. WHILE DOING LNDGS; MY STUDENT COMPLAINED OF FEELING DIZZINESS; SLIGHTLY SICK; AND A HEADACHE; AND ASKED ME IF I COULD TURN THE HEAT DOWN TO SEE IF COLD AIR COULD MAKE HIM FEEL BETTER. I IMMEDIATELY REALIZED THAT WE WERE BOTH EXPERIENCING SYMPTOMS OF CARBON MONOXIDE POISONING. I IMMEDIATELY TURNED OFF THE HEATER AND OPENED ALL THE FRESH AIR VENTS IN THE ACFT TO FULL. WE DEPARTED THE AREA AND RETURNED TO ZZZ AS FAST AS POSSIBLE AND AT LOW ALT TO COMBAT ANY FURTHER SYMPTOMS OF HYPOXIA. BOTH OF US FELT BETTER ONCE THE FRESH AIR STARTED FLOWING. I WAS GLAD THAT I HAD RECOGNIZED THE SYMPTOMS EARLY ENOUGH THAT NEITHER OF US HAD SEVERE SYMPTOMS AND THAT WE COULD RETURN TO ZZZ.