Background Implantable cardioverter defibrillators (ICDs) are recommended for patients at high risk of sudden cardiac death or for survivors of cardiac arrest. All ICDs combine a shock function with a pacing function to treat fast and slow heart rhythms, respectively. The pacing function may be very sophisticated and can provide so-called cardiac resynchronisation therapy for the treatment of heart failure using a pacemaker (cardiac resynchronisation therapy with pacemaker) or combined with an ICD [cardiac resynchronisation therapy with defibrillator (CRT-D)]. Decision-making about these devices involves considering the benefit (averting sudden cardiac death), possible risks (inappropriate shocks and psychological problems) and the potential need for deactivation towards the end of life. Objectives To explore patients?/relatives? and clinicians? views/experiences of decision-making about ICD and CRT-D implantation and deactivation, to establish how and when ICD risks, benefits and consequences are communicated to patients, to identify individual and organisational facilitators and barriers to discussions about implantation and deactivation and to determine information and decision-support needs for shared decision-making (SDM). Data sources Observations of clinical encounters, in-depth interviews and interactive group workshops with clinicians, patients and their relatives. Methods Observations of consultations with patients being considered for ICD or CRT-D implantation were undertaken to become familiar with the clinical environment and to optimise the sampling strategy. In-depth interviews were conducted with patients, relatives and clinicians to gain detailed insights into their views and experiences. Data collection and analysis occurred concurrently. Interactive workshops with clinicians and patients/relatives were used to validate our findings and to explore how these could be used to support better SDM. Results We conducted 38 observations of clinical encounters, 80 interviews (44 patients/relatives, seven bereaved relatives and 29 clinicians) and two workshops with 11 clinicians and 11 patients/relatives. Patients had variable knowledge about their conditions, the risk of sudden cardiac death and the clinical rationale for ICDs, which sometimes resulted in confusion about the potential benefits. Clinicians used various metaphors, verbal descriptors and numerical risk methods, including variable disclosure of the potential negative impact of ICDs on body image and the risk of psychological problems, to convey information to patients/relatives. Patients/relatives wanted more information about, and more involvement in, deactivation decisions, and expressed a preference that these decisions be addressed at the time of implantation. There was no consensus among clinicians about the initiation or timing of such discussions, or who should take responsibility for them. Introducing deactivation discussions prior to implantation was thus contentious; however, trigger points for deactivation discussions embedded within the pathway were suggested to ensure timely discussions. Limitations Only two patients who were prospectively considering deactivation and seven bereaved relatives were recruited. The study also lacks the perspectives of primary care clinicians. Conclusions There is discordance between patients and clinicians on information requirements, in particular the potential consequences of implantation on psychological well-being and quality of life in the short and long term (deactivation). There were no agreed points across the care pathway at which to discuss deactivation. Codesigned information tools that present balanced information on the benefits, risks and consequences, and SDM skills training for patients/relative and clinicians, would support better SDM about ICDs. Future work Multifaceted SDM interventions that focus on skills development for SDM combined with decision-support tools are warranted, and there is a potential central role for heart failure nurses and physiologists in supporting and preparing patients/relatives for such discussions.