XPath Parsing

I am trying to use XPATH to extract the Section after the Header having a value of ‘Sub Classes’

<Section>

<Header>Sub Classes</Header>

<Section>

<Header>Chemical</Header>

</Section>

Is there a way to do this using XPATH? I have tried a few different variations such as “Header[Header=‘Sub Classes’]/Section”, but only get a blank cell. I am not that familiar with xpath, thank you!