This temple is at Mattom in Alappuzha District on the banks of the Achankovil River. Lord Narasimha is worshipped in the idol of Mahavishnu with four hands. This temple has been mentioned in Unnuneeli Sandesham, composed long ago and in Unneeyachee Charitham composed in the 14th century. The place name Mattom is mentioned in both of them. The capital was shifted to Kayamkulam during the reign of the last ruler of the Onaatt royal family. Even then the rulers of Kayamkulam continued to worship Mattam Narasimha Moorthy. King Marthandavarma of Thiruvithaamkoor wanted to annex Kayamkulam to his state. He could add Chempakassery, Thekkumkoor and Vadakkumkoor more without any difficulty. But in two battles with the King of Kayamkulam, Marthndavarma was defeated. His ministers attributed the defeat to the blessings that the King of Kayamkulam received from Narasimha Moorthy.  Achutha Varier, the Minister of the King was killed in a secret move by Ramayyan, the minister of Marthandavarma. Ramayyan then wanted to take away the idol from the Narasimhaswamy temple. When they reached the temple on a night the poojaris and other workers in the temple could not withstand their attack. Still, the chief priest hugged the idol tightly to prevent it from being taken away. But Ramayyan cut off his head and after killing the other men there took the idol to Martandavarma. That idol is still seen in the temple near the famous Padmanabaswami temple in Thiruvananthapuram. A new idol of Mahavishnu was consecrated in the temple later and worshipped as Narasimha Moorthy. Devotees believe that worshipping here will save one from debts and diseases.