This page provides the Moola Mantra of Lord Vishnu. Moola Mantra is considered very effective among all Mantras. The Moola Mantra of the deity is most effective in Yantra Sadhana of the deity.
ॐ नमोः नारायणाय॥
Om Namoh Narayanaya॥
Om, I bow to Lord Narayana or Lord Vishnu, He is the preserver and the protector of the universe.