We must experience the feeling of something which can vanish to conclude that the transformation between sadness and happiness is by a Mantra prescribed as "Gathe, Gathe, Paramgathe, Parasamgathe, Bodhi Svaaha", "Going, Going, Gone, Gone forever, Enter the Divine Buddha".
Instantly we feel transformed. It is as though we have been struck by a ray of Enlightenment in a manner causing an awakening. It is a feeling of having come out of pitch darkness into a bright opening at an instant. One can only imagine if that feeling could stay with you indefinitely.
I was feeling sad yesterday, but today how can it be so different? How? -- I kept thinking repeatedly. How could it happen so quick, and what did I say, or do, which could have caused my sadness to vanish? -- These questions rang loud in my Mind.
I felt a deep sense of elation, choked that I could see what I had desired so much to go back to, and feeling so happy that I was able to climb to the top of the mountain. I had no idea standing at the base of a mountain where the top of the mountain could be, and how long I should feel and experience mental anguish, and the pain and suffering caused by our natural Karma.
This experience makes me conclude therefore, that the Heart Sutra is the prescription for the complete cessation of all cause and effect. If there is no cause, then there is no effect. If there no perception of any kind, there is no cause or effect.