The main Pratishtha (deity) at the Peruvanam temple is Irattayappan. The name came because the idol, which is a Swayambhoo( appeared on its own and not built by man), is of twin Sivalinga. Irattayappan stands for Lord Siva for the majority. Many believe him to be Sankaranarayana (Siva and Vishnu together). There are others who worship him as Ardhanareeswara (embodiment of Siva and Parvathy in one single form) and yet others to whom He is Umamaheswara (Siva in the company of Parvathy).
The Pooja is done for Siva alone which is different for the other three mentioned forms. Irattayappan is considered to be a benevolent deity, always loving the devotees irrespective of their failings. The sanctification was done by sage Pooru through the installation ceremony (PratisTha).
The Vandana Slokam (prayer) for Irattayappan is:
Sivam Sivakaram Saantam Sivaalmaanam Sivottamam (capital S for the first of the three Sa, sha and sa) Sivamaarga praNetaaram praNatosmi sadaaSivam (capital N for na in the third group- Ta, Tha, Da, Dha, Na and small n in the fourth – ta,tha,da,dha,na)
Siva means the embodiment of goodness or welfare. I pray to (praNatosmi) Siva, who converts everything to goodness (Sivakaram), is the embodiment of peace (Saantam), is the soul of goodness (Sivaalmaanam), the best among those who create welfare (Sivottamam), leads one through the right path (Siva maarga praNetaaram) and who is always the doer of good (sadaaSivam)