Push a stream of air from your throat through your open mouth. No tongue or lip contact.

Americans pronounce heatwave as HEET-wayv (/ˈhitˌweɪv/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "The heatwave made it almost impossible to go outside comfortably".
Record yourself saying "heatwave" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 6 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Push a stream of air from your throat through your open mouth. No tongue or lip contact.

Pull the corners of your lips back slightly. Arch the middle-front of your tongue high toward the roof of the mouth.

Touch the tip or front edge of your tongue to the roof of your mouth just behind your teeth. Keep your jaw relaxed. Stop the air, then release with a puff.

Round your lips into a tight circle. Lift the back of your tongue toward the soft palate and add voice.

Start with your jaw slightly open and the front of your tongue forward and slightly up. Glide upward, your jaw closes a little more and your tongue arches higher toward the roof of the mouth.
Lift your bottom lip so its inner edge (where the wet part meets the dry part) touches the very bottom of your top front teeth. Add vocal cord vibration as you blow air through.

The textbook way isn't wrong — it's just not how anyone actually says it.
In "heatwave", the "t" is not released — the articulators get into position but hold without the burst of air. Air stops but there's no release burst — the articulators hold position.
Stress falls on the first syllable, not the others. Stretch HEET — keep everything else short and quick.