Ida, Pingala and Sushumna are the three important Nadis in the body. Ida is the Chandra-Nadi. It cools the body. It flows through the left nostril. Pingala is the Surya-Nadi. It heats the body. It flows through the right nostril. Sushumna Nadi flows through both nostrils. It helps meditation. It is Agni-Nadi.
By Swami Sivananda, from the Book Amrita Gita. Swami Sivananda lived from 1887-1963. He was one of the great Yoga Masters of the 20th Century who made Yoga available to a great public. Copyright of the texts of Swami Sivananda The Divine Life Society Rishikesh