The left ring finger has a vein that directly connects to the heart and is called so for that.
Wedding rings are worn on the left ring finger because it is the only finger that has a vein connecting directly to the heart.
Hoax or Fact:
This is an age old traditional belief which says the ring finger of our left hand has a vein which connects it directly to the heart, and this is why it is called the wedding ring finger. Well, this is not so fact.
History of Ring Finger
The word 'ring finger' appears to have been derived from an ancient belief that it is a magical finger, which is why it is named after magic or rings. Declaring one's love and commitment by exchanging rings has been a tradition that goes back to the period of Ancient Egyptians. The ancient Egyptians believed that the fourth finger on our left hand had a vein that leads directly to the heart. So they used to believe that by placing a ring on this finger, the affections will be bound and cannot escape through the finger tips.
This symbolic belief of binding love through the vein in the ring finger to the heart passed on from ancient Egyptians, and after many generations, the Romans called it as Vena Amoris or "Vein of Love". Then in 1549, King Edward VI of England declared that the third finger (counting from the right, excluding the thumb) on the left hand would be the official ring finger, and in the same year, the Book of Common Prayers designated the left hand as the marriage hand.
Since then married couple symbolically declare their eternal love and commitment for each other by exchanging rings. However, in some of the modern countries, the wedding ring is worn on the ring finger of the right hand, and this practice is becoming more common now.
No Special Vein in Ring Finger
Unlike this popular traditional myth, there is no special vein in the ring finger of the left hand that connects to heart. All the fingers in our hand have a similar vein structure. The claim in question was just a belief that started before the medical science discovered how human circulatory system worked, and found its way into modern culture.
The claims being hoax, rings don't really bind two people together, it's their hearty feelings for each other! Isn't it?