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The Chen (Deep) pulse is not felt with light pressure but is obtained only with heavy pressure. All pulses such as Xi (Fine), Shi (Full), Fu (Hidden), Lao (Taut), and Ruo (Weak) belong to the category of Deep pulses. They do not resemble the Shi (Full) pulse, which feels vigorous under light lifting of the fingers, nor the Fu (Hidden) pulse, which is concealed within the sinews and bones. (This passage is from Zhang Lu. Additionally, the *Binhu Tizhuang Shi* [Poem on Pulse Characteristics by Li Shizhen] states: "Water flows downward; the pulse comes deep, soft, smooth, and even between sinews and bones; in women at the Cun position and in men at the Chi position, it is called 'Peaceful' across the four seasons." The *Xianglei Shi* [Poem on Similar Pulses] states: "The Deep pulse is naturally balanced between sinews and bones; the Hidden pulse requires pushing the sinew to reach the bone; Deep and fine like cotton is the true Weak pulse; Taut, long, full, and large is the form of the Lao pulse.") The Deep pulse indicates phlegm-fluids, cold pathogen causing failure of Yang Qi to rise, internal retention of water-qi, untransformed retained fluids, undigested food stagnation, rebellious Qi obstruction, and uncontrollable diarrhea; thus, internal conditions manifest as a Deep pulse. If the Deep pulse is accompanied by Fine, it indicates Shortness of Qi; if accompanied by Slow, it indicates Chronic Cold; if accompanied by Slippery, it indicates Undigested Food Stagnation; if accompanied by Hidden, it indicates Cholera-like colic pain; if accompanied by Rapid, it indicates Internal Heat; if Deep, Wiry, and Tight, it indicates Heart and Abdominal Pain. However, differentiation ultimately relies on whether the pulse is Forceful or Feeble. Generally, a Deep and Full/Forceful pulse is suitable for resolving stagnation and purging; a Deep and Deficient/Feeble pulse is suitable for warming and tonifying. (However, there are cases where a Forceful pulse requires warming, and a Feeble pulse requires purging; these have separate meanings detailed later and should be cross-referenced carefully.) If the pulse is Deep, Tight, and Rapid, accompanied by Headache, Fever, and Aversion to Cold, although the pulse is Deep, it still belongs to Cold Obstruction and should be treated as a Exterior Syndrome. How can it be generally considered an Interior Syndrome without using ascending and dispersing methods? (Zhang Lu said: When the pulse manifests Yin characteristics and is Deep, prolonged pressing makes it weaker. If Yang Qi is depressed and hidden, unable to float to respond to Wei Qi on the exterior, the pulse instead hides and becomes Deep, prolonged pressing does not diminish it. The mechanism of Yin/Yang and Cold/Heat lies in subtle distinctions. In Shanghan Disease, Deep pulses at both Cun and Chi positions indicate Shaoyin Meridian involvement. Therefore, distinguishing Yin and Yang among Deep pulses is the first critical step. Lin Zhihan said: One must understand that Deep pulses can indicate Exterior conditions. For example, when Cold closes the Couli (pores), blocking Wei Qi flow and causing sluggish Jing Qi, the pulse does not appear Floating but Deep; when Qi depression blocks the pulse, it appears Deep immediately upon palpation; when True Yin has been deficient for a long time and True Yang is exhausted, external pathogens enter directly due to deficiency, the pulse also becomes Deep; in these cases, the Deep pulse still belongs to Exterior Syndromes.)