The Pericardium is the most obviously constructed member of the twelve, and the tradition is fairly open about it. The earliest lists of organs give five yin and six yang, which does not pair evenly, and the eleven vessels of the Mawangdui manuscripts reflect that older arrangement. The twelvefold scheme that later became standard needed a sixth yin organ, and the Pericardium, the xin bao, the wrapping of the heart, supplied it.
That is not a criticism of the system so much as a description of how it was built. Chinese medicine is organised around correspondences in fives and sixes and twelves, and the pressure toward a number that divides evenly into the day, the elements and the yin yang pairs is visible throughout. The Pericardium is where the seam shows.
The role it was given, however, is a real one within the doctrine. It is the Heart Protector, the buffer that takes what would otherwise reach the sovereign organ, and its channel carries points the classical literature associates with the emotional life and with the chest. Its yang partner is the Triple Burner, the other member of the twelve with no straightforward anatomical referent, so the two anomalies are paired with each other.
The channel runs from beside the nipple down the middle of the inner arm to the tip of the middle finger, and its horary period is from seven to nine in the evening.