PSV & Ajax go goal crazy
Ibrahim Afellay opened the scoring on the stroke of half-time when he curled his shot inside the far post with Heracles already reduced to 10 men following a straight red card for goalkeeper Martin Pieckenhagen.
Hungarian Balazs Dzsudzsak doubled the lead early in the second half before Ola Toivonen and Jagos Vukovic completed the scoring.
PSV stayed one point behind former England manager Steve McLaren's Twente Enschede, who beat Vitesse Arnhem 1-0 on Saturday.
Third-placed Ajax Amsterdam thrashed Heerenveen 5-1 with all the goals coming in an extraordinary first half.
Demy de Zeeuw struck twice early to put Ajax on track and Uruguay forward Luis Suarez, the championship's leading scorer, converted a penalty for his 17th of the season.