Nick Heath: How open-source software could save your life

Karen Sandler's heart condition means she lives with what she describes as a "very high risk of suddenly dying".

Because of the danger her abnormally large heart could suffer a cardiac arrest she has been fitted with a combined pacemaker-defibrillator.

Encoded in this parcel of electronics are instructions for when to deliver a shock to correct potentially-fatal irregularities in her heart beat.