In traditional Chinese medicine, communication between the Heart and Kidney is essential for emotional, mental, and physiologic stability. This relationship is described as “harmony between Heart and Kidney,” or the harmonious balance between Fire and Water. Dynamic communication between these two Zang organs depends on the balanced descent of Heart Yang from the Upper Jiao to warm and support the Kidney, and the ascent of Kidney Yin from the Lower Jiao to nourish and cool the Heart. When Water rises and Fire descends appropriately, Yin and Yang remain balanced and the Shen is normal. Disharmony between the Heart and Kidney (Xin Shen Bu Jiao), is commonly observed in veterinary patients with behavioral disorders. Two common root (ben) patterns include Kidney Yin Deficiency with Heart Fire Hyperactivity, and Kidney Qi-Yang Deficiency with Heart Fire Hyperactivity. These patterns rarely occur in isolation and are often accompanied by secondary pattern disharmonies, including Liver Yin and Blood Deficiency, Liver Qi Stagnation and Liver Fire, Spleen and Heart Qi-Yin Deficiency, Phlegm Fire Misting the Mind; and in cognitive dysfunction, Brain Qi-Blood Stagnation. Layered patterns are common and should be expected rather than considered unusual. This paper reviews the physiology and pathophysiology of the Heart-Kidney relationship in Chinese medicine, how they parallel conventional concepts of Heart-Fire imbalance, and the common causes of Shen Disturbance associated with impaired Heart-Kidney communication.