God Viṣṇu(Vishnu) is sometimes referred to as Īśa (Isa) —
“yastaṁ nato’smi puruṣottamasādyamīśam” —
However, here ‘Īśa’ perhaps denotes the Almighty, the Ruler of all the universe and spheres– it is in this sense that Supreme Divinity is attributed to God Viṣṇu, as it is said in Śvetāśvetara Upaniṣad (Swetaswetara Upanishad) and Bhagavadgītā (Bhagavadgita)–
*vyākatāvyāktaṁ bharate viśvamīśam …
*prasādaye tvāmahamīśamībhyam.