Keyword rich sub headings

[staffjam]

Hi,

I'm in the process of having articles written and was wondering about the use of keyword rich sub headings.
Do the SE's pay much attention to these, and is it a good thing to focus on?
I realise keywords in the text are improtant, but i heard somewhere that sub-headings were even more important.

Also - if the article title is: Ethical issues of cloning, should i repeat this in different ways, e.g. Should we worry about the ethical issues of cloning.
Or can i have sub headings of Human cloning, animal cloning - or will these be disregarded by the SE's as being irrelevant and not relating to the title - even is in their own right they are very popular search terms with little competition.

Thanks for any advice.