10 Things That Make No Sense In Doctor Who
9. The Doctor's Missing Heart (The Edge Of Destruction)
On several occasions, it's been mentioned that Time Lords have two hearts, and this has always been a concrete part of Doctor Who mythology... or has it?
In the opening moments of the First Doctor serial The Edge Of Destruction, the TARDIS goes haywire and the Doctor collapses to the floor. Shortly after, Ian inspects him to make sure he's alright, declaring that his breathing seems regular, and that his heart - his one, single heart - is fine.
Flash-forward to the Third Doctor's debut in Spearhead From Space however, and we see an x-ray of the Doctor that clearly shows two hearts, and that's how it's been in every future episode: all Time Lords have a binary vascular system.
The First Doctor's missing heart has since gone unexplained, and though the obvious answer here is that the production staff hadn't yet thought to give Time Lords a unique biology, there's been little in the way of an in-universe explanation for this inconsistency. Instead, it's generally theorised by fans that Time Lords don't gain their second heart until after their first regeneration.