The Heart channel is the shortest of the twelve, with nine points, and it runs a modest course from the armpit down the inner arm to the little finger. That brevity is doctrinally loaded. In the account Chinese medicine gives, the Heart houses the shen, usually translated spirit or consciousness, and is described as the sovereign among the organs, the one whose disturbance disturbs everything. A ruler, in the metaphor the classics use throughout, does not do the work himself.
The tradition draws a practical consequence from this that has no parallel elsewhere in the scheme. The Heart is held to be too important to be approached directly, and the Pericardium, the Heart Protector, is described as receiving on its behalf whatever would otherwise strike it. Much of what a reader might expect to be treated on the Heart channel is therefore treated on the Pericardium channel instead, and the classical texts say so explicitly.
The Heart pairs with the Small Intestine as the yin and yang of the Fire phase, and takes the horary period from eleven in the morning to one in the afternoon, the height of the day, which the scheme treats as fitting for the ruler.
All of this is a description of what the tradition holds. The atlas asserts nothing about cardiac function and offers no guidance; anything concerning the heart as an organ is a matter for a clinician.