General ⇒ Left justify single line?

[fuego]

I'm writing a document and I'd like to have single lines left justified, e.g. section headings and don't want to use the LaTeX section headings. Is there a way to do this? When I try, it left justifies the entire document. Thanks.

[phi]

Please give a more precise description. If you write a paragraph that consists only of one line, this line is automatically left justified.