I have read from abhidhamma book saying that our thoughts generate inside heart and heart is invisible to naked eye and untouchable. this statement in abhidhamma can't be accepted with modern day science. my certain question is when heart transplant took place what happen to person's thoughts? will the thought of heart owner transfer to the patient? Can someone give proper explanation on this?
Heart (Sanskrit hridaya) also means mind. The same is true for Chinese Xin, Japanese Kokoro and the like. The etymology might be: hrid - center, ayam - this. In Tantric Buddhism it is said that heart, or more precisely "Heart center" is located in the center of the chest, on the central channel. It is considered to be the seat of mind, or "the seat of Pure Consciousness". Similar views can be found in Hindu yoga, Taoism and other ancient teachings.
It is said that the central point of mind can move up and down along the central channel, and when unwholesome emotions arise, such as greed or anger, it shifts to the left or to the right from the central channel.
More details can be found in Tibetan Buddhist literature.
So I guess that the text you mentioned speaks not about the physical heart. And I think that modern knowledge of anatomy or physiology does not invalidate these views, because they are the result of contemplation of energies by means of our feelings. Even if modern science "doesn't know those kinds of energies", it's clear that our feelings can be interpreted as movements of energy.
For example, we might say: "I felt all my energy drained", or "Seeing that smile I felt that new fresh energy fills me", and the like. If you think about it, these feelings are not less real perceptions than what we see with our eyes. So they don't need to be kinds of physical energy, it's enough that they are real as our perceptions, and their knowledge can be used in training our mind and improving our lives.
PS. Some interesting references:
Abhidhamma says heart base. This is physically in the areas where the heart is but not necessary the physical organ. This is where mind resides in a pint point area where the heart is, through the body functions are controlled by the brain.
If a heart transplant takes place it is the physical organ which is changed. It is not the mind which is changed which depends on the materiality of the heart's location. Therefore heart base does not change with heart transplant. Also the mind is not physical though it depends on materiality of the location. When the new heart is put in would operate based on the materiality of the new heart.
Both, brain and heart, are not important in buddhism, because arūpabhramma has not both.
So in buddhism, brain and heart are not important.
Brain and heart are just mechanism, that are arised by consciousness.