I have to write two lines of poetry in iambic tetrameter and I am not sure if this is correct or not. Any help would be greatly appreciated!

with heavy hearts untwine ourselves
yet midnight orbs demand I stay

Thank you!

Yes. Those two lines are in iambic tetrameter. :-)

http://en.wikipedia.org/wiki/Iambic_tetrameter

thank you very much, Ms. Sue! Have a wonderful day!

Your attempt at writing two lines of poetry in iambic tetrameter is close, but there are a few small adjustments needed for it to be completely correct.

Iambic tetrameter consists of four metrical feet, with each foot containing an unstressed syllable followed by a stressed syllable. So, in each line, you need to have four pairs of unstressed and stressed syllables.

Here's how I would suggest revising your lines:

From heavy hearts, untwine ourselves (unstressed, stressed, unstressed, stressed)
Yet midnight orbs demand I stay (unstressed, stressed, unstressed, stressed)

In these revised lines, you have four metrical feet in each line, and each foot follows the unstressed-stressed pattern of iambic meter.

Feel free to adjust or experiment further to achieve the desired rhythm, but these revisions should provide a good starting point for writing in iambic tetrameter.