According to my point of views " A trader's heart " is his decision making power and accuracy of the decision he/she make. 
I think a good trader should not take decision using his heart because a heart gets worry faster than a brain so I think in trading feelings and emotions are not allow, but those who has a patient heart most of time they use to earn good money, I trader heart should be strong enough to face all kind of situations, if the price falls one should convince his heart that soon the price will be high, buy logically in trading it is good to use your brain instead of your heart.