Ischnura heterosticta is a small damselfly. Males have body length around 34 mm, strikingly blue and black with a mostly dark, unringed abdomen except at its very base and the distinct blue tail tip. Distinct unbroken lateral blue markings on thorax, blue antehumeral stripe and two obvious postocular spots, one behind each eye. Eyes bicoloured: black above and blue below.

The females are the same size, have a variety of forms including green, brown, black, and a form with very similar colourings to the male. As with other species in this genus, elsewhere in the world, females have several colour morphs. So far, four types have been recorded: a green morph; brown morph; purplish morph; and a blue male-like 'andromorph'. All have a distinct antehumeral stripe and the distinct pale postocular spots. 

The species is most similar to A. watsoni but the latter is much smaller, with a green antehumeral stripe and lacks the postocular spots.