Does the heart play a role in the occurrence of emotions? It is a common belief that the heart is somehow related to emotions. When we are nervous,our heartbeat is effected (increased heart rate) and when we are happy, another pattern in heart function can be observed.

My question is the following. Does the heart have a significant role in the occurence of emotions, or is it that the heart is just an organ that pumps blood and these physiological changes are merely a by-product of processes relevant to emotion?
Is the heart's function of interest to any cognitive scientific field of study?
As it has been pointed in the other answers and the comments, the heart is indeed only an organ that pumps blood and all the processes responsible for emotions are carried out by the brain. However, the heart and generally the autonomous nervous system is of critical importance to somatic theories of emotion. These theories propose that bodily responses in the presence of a certain stimulus, initiate emotional processing. However, it is not that the heart, for instance, creates an emotion. It is the brain that notices any significant physiological changes like the heart rate being increased and makes an interpretation of this internal state taking into account the available stimuli. This idea originates with William James' theory of emotion but it was also incorporated in more recent approaches like the somatic marker hypothesis by Antonio Damasio.