The major responsibility of the heart in TCM is housing the mind and controlling the shen. “Shen” can be seen as the overall healthiness of the mind. When you look at a healthy person in good spirits, you know how you can see that in their eyes? There is a certain bright clarity and sense of health that shines from within. We acupuncturists would say that this person has good shen.
Have you ever looked into a person’s eyes and noticed they seemed, well, not all together? Maybe their eyes were shifting from side to side, or maybe they just seemed cloudy and dull, as if they were not really in the present moment. Perhaps they seemed dazed or confused. This is poor shen. Sometimes mild depression or distraction can cause this shen disturbance; if very severe, it can manifest as mental illness, such as schizophrenia.
One of my professors once described the heart’s job as maintaining appropriate timing in life. He used an example of a person wearing a bathing suit. If this person wore the suit out to the pool in the summer, his heart was doing its job. But if he put the bathing suit on for a business meeting, it meant the heart was not allowing him to make the right choice for the circumstances. In short, the Heart is all about maintaining the correct behavior for specific situations. Think about behavior patterns you might see in the case of mental illness: inappropriate speech or tone of voice, making unsafe decisions, misjudging situations and social cues.
The heart is not about moderation; it is an organ of extremes, from wild joy to crushing lows. Extreme joy may seem like a positive thing, but this is the type of joy unsustainable and it burns out quickly. Think of manic-depression: manic highs, followed by deep depression. Both depression and anxiety are linked to the heart. ADHD is also considered to be a result of heart imbalance; the hyperactivity is a result of the heart not properly controlling the mind.