You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <querypage qpoffset="10" />
  </query-continue>
  <query>
    <querypage name="Ancientpages">
      <results>
        <page value="20150813130543" timestamp="2015-08-13T13:05:43Z" ns="0" title="Sociedad Argentina de Cardiología" />
        <page value="20150922153258" timestamp="2015-09-22T15:32:58Z" ns="0" title="Antiplaquetarios" />
        <page value="20150922154125" timestamp="2015-09-22T15:41:25Z" ns="0" title="Tratamiento para las arritmias" />
        <page value="20150930194724" timestamp="2015-09-30T19:47:24Z" ns="0" title="Fibrinolíticos" />
        <page value="20151013205838" timestamp="2015-10-13T20:58:38Z" ns="0" title="Fiebre reumática" />
        <page value="20151026153020" timestamp="2015-10-26T15:30:20Z" ns="0" title="Tratamiento para la angina de pecho" />
        <page value="20151027153548" timestamp="2015-10-27T15:35:48Z" ns="0" title="Tratamiento para la hipertensión pulmonar" />
        <page value="20151029234850" timestamp="2015-10-29T23:48:50Z" ns="0" title="Síndrome de Marfan" />
        <page value="20151106134535" timestamp="2015-11-06T13:45:35Z" ns="0" title="Cardioversión" />
        <page value="20151106190654" timestamp="2015-11-06T19:06:54Z" ns="0" title="Dinitrato de isosorbide" />
      </results>
    </querypage>
  </query>
</api>