In a book that I am reading, there are a couple of breathing rhythms that the author recommends for building up one's Prana to heal others. The one that he recommends is the 6-3-6-3 rhythm, if I recall correctly. Are there any other breathing rhythms that would also be optimum for healing?

I think I've read that book before. It's a good starter for learning about how to restore and replenish the Chakras through pranic healing. I personally prefer the 7-1-7-1 breathing rhythm because it's very powerful!