When there are no page numbers but paragraph numbers are visible, use the abbreviation para.
Basu and Jones (2007) went so far as to suggest the need for a new “intellectual framework in which to consider the nature and form of regulation in cyberspace” (para. 4).
Cite the heading and the number of paragraphs where the quote is located.
In their study, Verbunt, Pernot, and Smeets (2008) found that “the level of perceived disability in patients with fibromyalgia seemed best explained by their mental health condition and less by their physical condition” (Discussion section, para. 1).
If the heading is too unwieldy – shorten it.
“Empirical studies have found mixed results on the efficacy of labels in educating consumers and changing consumption behavior” (Golan, Kuchler, & Krissof, 2007, “Mandatory Labeling Has Targeted,” para. 4).
The heading was “Mandatory Labeling Has Targeted Information Gaps and Social Objectives.”
(American Psychological Association, 2010, pp. 171-172)