HIS Alternative II - UK Site

This trial is comparing a new type of pacemaker technology (His-Purkinje conduction system pacing) with standard biventricular pacing (CRT) for people with heart failure and a weak heart that hasn't responded to medication alone. **You may be eligible if...** - You are over 18 with heart failure and a weakened heart (ejection fraction of 35% or less) - Your symptoms are moderate to severe (NYHA class II–IV) despite being on the best medical treatment available - You have sinus rhythm and a specific type of electrical conduction delay (left bundle branch block) - You are being planned for a new CRT device, OR an upgrade of an existing pacemaker to CRT **You may NOT be eligible if...** - Your ejection fraction is better than 35% - You don't have a left bundle branch block or similar conduction abnormality - You are already on optimal CRT therapy - You have other conditions making device implantation too risky Talk to your doctor to see if this trial is right for you.