Heart

In Traditional Chinese Medicine (TCM), the Fire element has two meridians associated with it which means a little more complexity than the other elements.  The Yin aspect of one meridian is associated with the Heart and the other meridian is associated with the Pericardium.  On the Yang side, the Small Intestine and the Triple warmer partner the two Yin organs.  The Triple warmer or burner as its sometimes known is a Chinese concept which has no corresponding physical organ.  It's a little esoteric so I'll Google that one for you.  The heart sits behind and slightly to the left of the breast bone and ontop of the lungs and sits within the Pericardium, a  sack like membrane  The small intestine constitutes most of what we know as our bowels.  An adults is about 8m in length.  

Negative emotions of mania, over excitation and (believe it or not) too much joy can adversely affect the heart/pericardium.