Eugene says that in the average human lifetime the human heart beats 2 million times. Average lifespan is 70 years, 36,792,000 minutes. At 70 beats a minute that works out to 2,575,440,000 beats. For comparison your heart beats 3,024,000 times in a 30 day month.
The subtitles on the DVD are wrong when Ianto speaks at 12 mins. They read "Caernarfon" when he actually says Camarthen.
Gwen visits a science museum in Aberystwyth while investigating Eugene's death. There is no science museum in Aberystwyth, nor are there any buildings large enough to house the exhibition seen in the show.