There were some good moments in the latest Doctor Who story - The Power of Three, although it was basically a kiddie friendly version of Clive Barker's Hellraiser. What stood out for me was, of course, the stuff about hearts and the Doctor's dual cardiovascular systems. As UNIT descended upon the Ponds' house Kate Stewart identified the Doctor by his dress sense and then confirmed this with a hand held heart scanner producing a wonderful screen shot. (Click on the image for a larger picture.)
There we are, a nice colour image of two hearts. Unlike some of the previous images we have seen the hearts are shown arranged one above the other rather than side by side. We also see what could be lungs highlighted in blue, or this may be the Doctor's famous respiratory bypass system - a convenient "get out of jail card" for the writers on several occasions. There are also some rather truncated ribs which are helpfully kept out of the way of our view of the middle. Quite how this scanner manages to show them at the sides and not where they meet at the breastbone is a mystery but UNIT get all the cool toys.
Things take a turn for the worse when the mysterious cubes stop a lot of people's hearts. This also affects the Doctor's left heart and he struggles to continue with just one side beating. As his condition deteriorates Amy takes matters into her own hands and grabs a conveniently placed defibrillator from a hospital corridor. She shocks the Doctor and restarts his left heart. The reinvigorated Doctor can then program the cubes to act as some form of mass defibrillator and restart the hearts of all the affected humans. Happy endings all round.
Unfortunately this plot device makes the usual television error about what defibrillators actually do. When the heart is fibrillating it means that the muscle is contracting in an uncoordinated fashion and not pumping blood effectively. If you could look directly at a fibrillating heart it would be quivering rather than contracting regularly. Defibrillation applies an electrical shock which basically resets the electrical system of the heart and hopefully gets it contracting properly. If the fibrillation continues unchecked then eventually the heart stops altogether, at which point an electrical shock is going to make no difference at all. Sadly you can't "jump-start" a stopped heart with a defibrillator.
The Doctor's heart and the hearts of a third of the world's population have stopped. Defibrillation will not restart them. In fact using the defibrillator as Amy does would actually risk causing fibrillation in the Doctor's other heart. It is also interesting that the machine she uses is a rather old fashioned model that would only be used by doctors (of the human kind) or trained paramedics. You are much more likely to see something called an Automated External Defibrillator in public places or hospital corridors.
There is another problem. When the Doctor's left heart stops he still has his right sided organ to continue pumping blood to his brain. The humans who we see collapsing all around the world do not have this luxury. While their hearts are stopped no blood is getting to their brains so they are all at risk of serious brain damage. Unless I missed the bit where the Doctor managed to go back in time and somehow restart their hearts immediately after they collapsed then I don't think we would see people just standing up and carrying on as if nothing had happened.
However, the misconception about defibrillation is very common in film and television so the writer can perhaps be excused for making the same mistake. At least this episode gave us a nice view of the Doctor's two hearts. It also get brownie points for introducing Kate Stewart who I hope we see more of, and for mentioning the Zygons. Apart from that I found all the stuff about the Doctor living with the Ponds rather dull and that combined with the poor medicine made it rather a weak story for me. We shall see if the Weeping Angels can save the current series.