Be relaxed and sit with you spine straight and eyes closed, watching your breaths entering and leaving your nostrils as you breathe normally for a minute.
Then inhale slowly and deeply and hold the breath as long as you can comfortably, releasing it deliberately in a controlled manner.
When the exhalation is complete, close the right nostril with your right thumb and inhale deeply through the left nostril, visualizing the prana fill every cell in your body with pure energy.
When the inhalation is complete, hold your breath for a slow count to five.
Now open your right nostril by removing your right thumb and close the left nostril with your right forefinger, releasing the breath slowly but naturally through the right nostril.
When the exhalation is complete, hold your breath to a count of five and experience the no-breath calmness.
When you are ready to breathe in again, breathe in through your already open right nostril, keeping the left closed with your forefinger and hold as before to a count of five.
Then release your forefinger, exhaling through the left nostril as you close your right nostril again with your right thumb.
Repeat this cycle up to twenty times but as with all pranayama exercises, let your body be the judge and stop if you ever feel you are pushing too hard.
At no time during this exercise do you need to force your inhalation, exhalation or holding of breath and everything should be as normal as possible, the only thing different from breathing unconsciously being that you are now consciously and deliberately controlling every breathing action.
Nadi ("nerve") Suddhi ("cleaning") is the best pranayama exercise to slow down the heart rate whenever you need to do this, particularly before beginning a meditation session.
It calms and focuses the mind very quickly.