Do zombies' hearts keep beating?

This has been zombie week in my world. Last Saturday I went out to a Zombie Birthday Pary (Celebrating 34 years of being alive! That's 34 years of being undead!). Then on Wednesday, I learn through Twitter and various podcasts that it's Zombie Preparedness Awareness Day, a day to review your plans and supplies to ensure you're prepared for the inevitable zombie attack. And last night we went to see a zombie movie at the Parkway. It wasn't great, but it was a nice bookend to my week.

All this undead energy around me took over my shower thoughts this morning, centered around the question: Do zombies' hearts keep beating? I would have to guess, "No," based on the fact that zombies, when torn apart, do gush blood. (The fact that humans use the fact that they can detect a heartbeat to declare that someone is still alive was ruled out as additional evidence because humans, when faced with the threat of having their brains eaten, are not known for clear and methodical thinking.) On the other hand, another defining characteristic of zombies is their ashen appearance, which can be expected to result from a lack of blood in surface capillaries, blood which would normally be pumped into that area by a beating heart.

Let's examine this second possibility a little more deeply: If the undead heart were to stop beating, then the blood would no longer be circulating, but would remain in the body until some outlet was created (e.g., the removal of a limb, a gunshot inexplicably aimed at the heart when we all know you kill zombies by shooting them in head). Zombies are not immune to gravity, so it seems to me that the blood would pool in their lower extremities. This may help to explain the dragging walk and the "lifeless" hand (actually just quite heavy now with all that extra liquid). If this is correct, then our cinematic representations of zombies really should more accurately reflect the corporal distortion which can be expected to result from this, namely very fat hands and feet -- almost clown-like, really, in their ballooned out state.

Of course, I am willing to entertain the possibility that the heart simply re-starts (after death) pumping at a super slow rate, thereby continuing to bring blood to the limbs to keep them animated, but not at a rate strong enough to drive the blood into the smallest regions of the vascular system.

None of this helps me understand the phenomena or appearance of fast zombies. They're just simply freaky and the creatures against which we must most strongly fortify ourselves.