This extra lead runs from the more easily accessible right ventricle of the heart, out of the heart and into the external vasculature of left ventricle, shocking it from outside the heart.

ECONOMIST: Case history

An LV lead (a thin, coated wire) is placed on the lower left chamber of the heart (the left ventricle) to stimulate the two sides of the heart to beat in synchronization with each other, which helps the heart to beat more efficiently.

FORBES: St Jude Withdraws Older LV CRT Leads From Market

But so far as its heart is concerned, he has no more than grasped its right ventricle.

ECONOMIST: Heads, not hearts

They are designed to help the pumping action of the left ventricle - one of the four chambers that make up the heart.

BBC: Image of heart failure