The heart has its own “brain.” Now, scientists have mapped out a detailed map of this little brain, called the intracardiac nervous system. The heart’s big boss is the brain, but nerve cells in the heart also have a say. These neurons are thought to play a crucial role in heart health, helping to fine-tune the heart’s rhythm and possibly protecting people against certain types of heart disease. But until now, this local control system has not been mapped in detail. Until recently, modern science perceived the heart as simply a pump that regulates the flow of blood in our bodies. But long before that, many cultures believed that the…