I would say my heart (in its own way) rules me. But I would say that the heart vs. head paradigm is a bit polarized. Intelligent, reasonable people can disagree on the best course of action to take in a given situation; and caring, loving people can disagree among themselves about the best tact to take in x situation.
Work in the neurosciences has turned up the fact that emotion is needed to power the brain to make any kind of decision, whether one thinks she is being "logical" or largely "emotional" or "sentimental."
I remember hearing, on NPR, a story about a man who had undergone brain surgery, and a part of the brain largely responsible for governing the emotions was removed. Now, ostensibly he became a creature of pure logic. After the procedure he would be shown pictures of horrible, gut-wrenching scenes, and all that, and they would elicit absolutely no response from this man.
Now, because of this deficiency, he ended up losing his high-powered corporate job. For example, he would spend hours trying to decide whether to sign a contract with the blue or the black pen (this question is outside the province of logic). At some point you have to "emotionally" say to yourself Just go for it, just do it. Make a decision, any decision!"