Nahush after falling from heaven lived on earth for many years as a giant python. Due to his size, he could not move much and would survive by eating whatever came his way.
During their final pilgrimage to Himalaya, Pandava came across the python. He caught Bhima in his grasp and despite using all his might Bhima could not escape the clutches of Nahush.
When Yudhishthira found out about the trouble Bhima had gotten into, he talked to the snake trying to convince him to let his brother go.
After having an enlightening conversation with the son of Dharmaraj, Nahush got released from the curse. He regained his original form and went to heaven.