Shu points are a very special group of five points on each meridian, except the Heart Meridian. Shu points were added to the Heart meridian in a later book called, Nan Jing, even though the Nei Jing takes the time to explain exactly why the Heart meridian does not have Shu points. Ling Shu chapter seventy-one makes the reason clear.
“黄帝曰：手少阴之脉独无输，何也？岐伯曰：少阴， 心脉也。心者， 五脏六府之大主也，精神之所舍也，其藏坚固，邪弗能容也。容之则心伤，心伤则神去，神去则死矣。故诸邪之在于心者，皆在于心之饱络，饱络者，心主之脉也，故独无输焉。”
“Huang Di asks, ‘Why is the Hand Shao Yin meridian the only one without Shu points?’ Qi Bo replies, ‘Shao Yin is the heart meridian. The heart is the master of five Zang and the six Fu’s great master, it is the spirit’s home, this organ is firmly protected, disease must not enter. If a disease enters the heart, it will be injured. If the heart is injured, the spirit leaves. If the spirit leaves, the patient dies. Consequently, the diseases related with the heart, fall upon the pericardium meridian. The pericardium meridian is controlled by the heart. Therefore, the heart meridian is the only one without Shu points.”
Nei Jing Eastern Medicine 