Cardiac resynchronisation therapy is also known as biventricular pacing, and aims to improve the heart’s pumping efficiency by making the chambers of the heart pump together. 25-50% of all heart failure patients have hearts whose walls do not contract simultaneously. CRT involves implanting a CRT pacemaker or ICD (implantable cardioverter-defibrillator) that has a lead positioned in each ventricle. Most devices also include a third lead which is positioned in the right atrium to ensure that the atria and ventricles contract together.