Beta-blocker tablets are an effective treatment for heart failure that make people live longer and reduce the need to be admitted to hospital. Many patients who are at high risk of death are prescribed beta-blockers, but later choose to stop taking them because of symptoms that they perceive to be side-effects. Some patients' symptoms may genuinely be side-effects due to the beta-blocker tablets, but, in reality, many of the symptoms which may lead to people stopping beta-blockers are actually experienced at similar rates compared to placebo. The symptoms may be caused by heart failure itself, or the expectation that they will have a side effect when they take a tablet (the nocebo effect). There is a need to be able to identify the majority of patients who aren't actually having side-effects so that they can restart beta-blockers and not miss out on life-prolonging treatment. To answer this question reliably and with high precision requires a personalised approach with an 'N-of-1' study. This study will measure participants' symptoms in three scenarios: taking a beta-blocker tablet (bisoprolol 2.5mg) or a placebo tablet or no study medication in a randomised order. The primary aim of this study is to determine, for an individual, whether the adverse effects of beta-blockade in heart failure are genuine. Specifically, the objectives are: 1. To determine the proportion of a patient's symptoms that are due to taking beta-blocker tablets, and the proportion that are due to the expectation that the treatment will cause symptoms (the nocebo effect). 2. To determine whether, on average, symptoms are worse when taking beta-blocker compared to placebo tablets or no treatment. 3. To determine whether on average symptom intensity associated with beta-blockade decreases after receiving a report on how much of their symptoms are due to the beta-blocker. Throughout the protocol participants report daily the intensity of the symptom that previously led to their beta-blocker cessation via a smartphone app. Participants will report weekly their adherence, general heart failure symptoms and quality of life. In this way the investigators will discover, for an individual patient, the proportion of their symptom that is due to the beta-blocker tablet, and whether knowing their personalised results helps them to restart beta-blocker tablets.