Pet lovers have always wondered: Who loves me more — my dog or my cat?

Everyone knows that dogs wear their hearts on their sleeves when it comes to the affection they show for their owners. Leave your house for the day (or for five minutes) and your dog will more than likely be waiting by the door with a wagging tail upon your return. A cat may or may not acknowledge your existence before returning to her nap.

Dogs live for the attention of their owners. They'll follow you around the house and curl up at your feet just to be close. Cats are more aloof, going about their business until they deem it acceptable for you to pet them. (Just not too much.)

But cat owners have always argued that their cats do love them, they're just more sophisticated in the ways that they show their affection.

So who loves you more? A new scientific study put both pets to the test and came up with a definitive answer.

As part of a new BBC2 documentary called "Cats vs. Dogs," U.S. neuroscientist Dr Paul Zak was asked to develop a "love test" to be used on pets. Zak decided to measure the amount of oxytocin — aka the love hormone — that was released by pets when they saw their owners.

"We have pretty good evidence that dogs actually love their humans,” Zak told the British newspaper, The Telegraph. "A couple of small-scale studies have shown that when owners interact with their dogs, the human and their dog appear to release oxytocin."

But up until now, this test had never been conducted on cats.

Zak's experiment was simple. He measured the oxytocin levels in the saliva of 10 dogs and 10 cats, 10 minutes before playing with their owners and then again immediately after. And the results in both cases were completely surprising.

Zak found that the hormone increased by 57.2 percent in the dogs after seeing their owners. That's huge and on par with the levels that a parent would have when interacting with her child. Yes, dogs do love us. Even more than we thought.

Not surprisingly, the cats' levels were lower — around 12 percent. But what is surprising is that cats really do love their owners. The prevailing theory was that cats merely tolerated their human companions. But Zak's study showed that the love is there.

So there you have it. Dog owners can revel in the knowledge that their pets really do love them more. While cat owners can take comfort in the knowledge that their cats really do love them at all.