Why this display property
display:inline
given to<h3> element:
Aggiornamenti inside this post in not properly executed :

<h3 style="display:inline" title="Nota dell' ufficio stampa dell' Inter sull' ufficializzazione della data e della sede dell Supercoppa TIM 2010 da parte della Lega Seria A">Aggiornamenti</h3> [ aggiornamento del 2-7-2010 h 22.02]

CSS W3schools reference
CSS Display and Visibility:
2nd & 3rd paragraph
CSS display Property

The WordPress editor puts an invisible <p> tag around the line after the <h3> element. Go into HTML view and make sure there are no line spaces between the <H3> and what follows.

The WordPress editor puts an invisible <p> tag around the line after the <h3> element. Go into HTML view and make sure there are no line spaces between the <H3> and what follows.

Sorry
but i ask to wordpress.org forum support and it seems it isn' t true.
Maybe you want to mean

Browsers automatically add an empty line before and after a heading.

as write in the Note below first example of HTML Headings in w3school HTML tutor
this isn' t an issue of wordpress editor.

Anyway bypassing that details about who add empty line after h1,
i took a wlook abouhat t you told me and there was no space.
At the moment css attribute display:inline wasn' t add to <h3>.
I'd like to solve/understan this situation.

i think because h3.inline inherits line-height from
css.php h3 rules of theme in use in my site that is atahualpa 3.44

....
h3 { font-size: 24px; line-height: 1.3; margin: 1em 0 .2em; }
...

Anyway teh propbel in not the extra line
BUT having h3 heading on the same row of following text:
PS
I try adding in line style attribute of <h3> mentioned : line-height:0; and also margin:0pt,
i.e. :

<h3 style="display:inline!importan;line-height:0;">

or

<h3 style="display:inline!importan;line-height:0;margin:0pt">

but no way to have heading and text on the same row.

@ STB 2nd
As you talked me about line-height it sound me strange:
cause if i set an element toi bi displayed as inline elemente that value will be cleared it's obviuosly.

The solution has been found:
add attribute display:inline to following <p>...
and everythings works fine without modifing no rules of <h3> ( only adding style="display:inline"
Take a look here.