A mudra, meaning a seal or lock, is a certain position or a definite way the fingers are held.
Mudra are used in many breathing exercises and in meditation. Vishnu mudra is the mudra used for basic pranayama.
Vishnu Mudra Position
With your right hand, extend the thumb, ring finger, and little finger, then fold the middle and index fingers toward your palm. Your left hand remains inactive at your side or on your left knee.
Vishnu mudra may seem kind of strange, and maybe you feel a little uncomfortable blocking off your nostrils with your fingers in the name of breathing. You don’t have to do this in a restaurant or phone booth; save it for yoga class or the privacy of your own home. The best way to acquaint yourself with this basic mudra is to practice with the Single Nostril Breathing Exercise (see page 49).