With help from Heaven we can understand that with what Rabbi Chaim Vital, of blessed memory, wrote (in Shaar Ruach HaKodesh), "Know that in the same way that through a person's pulse bodily sickness can be known and recognized to healers of the physical being, so, too, could my master [the Arizal], of blessed memory, diagnose sickness of the soul by feeling one's pulse…."
Within these pulses are secreted, hidden away…the supernal life-force of the Infinite One….
We have already expounded on the secret of the verse "all in wisdom you have made" (Psalms 104:24), that this "wisdom" spreads forth in the aspect of the blood vessels, crucial to the vital energy of a person, which is the aspect of the familiar types of pulse. For within these pulses are hidden and enclothed the supernal life-force of the Ein Sof [Infinite One], Who brings life to all of existence.
It is already known that "all becomes clarified via thought" (as is brought in the Heichalot section of the Zohar, parashat Pekudei) - that all "320 Sparks" become clarified via thought, the evil refuse departing from within the good. Thus the aspect of "good [i.e. pure] blood", which is the ideal vital energy, becomes hidden away in the pulse, and the "bad blood" leaves outside.
And sometimes because of a person's transgressions, one's power of thought is unable to clarify and expel the extra refuse of the blood outside. It is then that a person becomes sick and needs bloodletting treatments in order to allow [the blood] to exit, as is known by doctors who perform these bloodletting procedures. It is for this reason that all of a person's vital energy depends upon the pulse, and all illnesses can be diagnosed therein. For according to the degree of the transgression and sin that one makes, is the deficiency of the aspect of this "light" and vital energy within the pulse.
When one aspect dominates, it indicates a deficiency in that very same trait….
In the Tikunei Zohar it is written that there are ten types of pulse, each corresponding to the Hebrew vowels kamatz, patach, tzeri, etc. To elaborate, all vowels are [rooted] in chochma, as mentioned, and all the various rhythms of the pulse are all in the form of the [various] vowels. And when a person feels the pulse with his hand, sometimes there is found a pulse of one beat [in Hebrew, "nekuda", literally "vowel"] and afterwards a beat to the side - this is the [formation of the] vowel tzeri; and sometimes there is a singular beat which pulse above with another below it - this is the [formation of the] vowel shva; and sometimes there is a singular extended beat accompanied by a brief one - and these together form the vowel kamatz; and so it goes for all the vowels, each demonstrating according to the character of one's vital energy drawn at that particular time, each indicating from which aspect of chochma [it is rooted]. For example, if the pulse is in the form of the vowel kamatz, this indicates an imbalance [i.e. domination] of the sefira of keter [associated with the kamatz] within chochma, from which is sent forth vital energy and influence to all the various limbs at that time; and if the pulse is in the form of the vowel patach [associated with the sefira of chochma], this indicates that vital energy is being drawn from [the sub-sefira] chochma within chochma, etc.; and this applies to all the Hebrew vowels within the nine [upper] sefirot, as mentioned in the Tikunei Zohar. (Sometimes two vowels combine with each other, like shva-patach [or] shva-segol, etc.)
Through this, one can understand and know the nature of a person's sin….
One should know that through this [diagnoses via the pulse], one can understand and know the nature of a person's sin. [For example] if a person's pulse appears like a kamatz, this indicates that a he has sinned in relation to keter, and thus [keter] is dominating at the time, demonstrating that its [negative] force was unable to depart due to the person's sin [i.e. imbalance]. For we see that when one aspect dominates, it indicates a deficiency in that very same trait, in the same way as the verse states "You take away their breath, they perish" (Psalms 104:29) - that any weak thing attempts to bolster its strength in order to carry on. And sometimes it indicates the opposite, in that a person [may have] just performed a particular mitzvah within that trait, but there are none among us [now] who know exactly [how to judge this]. Thus far the holy language of our righteous [Rabbi Chaim Vital], of blessed memory.
So we find that the transgressions that a person commits have an effect on that person's pulse, and there they can be felt and recognized. All this was known, with the help of Heaven, by the Talmudic Sages. The Mishna says, "Whoever influences the masses to become meritorious - no sin will come via his hand" (Avot 5:18), instead of saying "won't sin", for this is to teach us that even if as a result of his own free will a person sins, in any case his causing the masses to become meritorious will protect him, and G‑d will forgive him immediately of that particular sin. And right before a particular transgression begins to have an effect on a person's hand, meaning the pulse, The Holy One, blessed be He, forgives him immediately - before the sin is detectable via his hand's pulse.
[Translated from Bircat Avot by Baruch Emanuel Erdstein]