Protocol Version 8 The following sections in the trial protocol have been amended. Section 1. Investigators, Section 2. Background and Rationale, Section 5. Eligibility Criteria, Section 6.1 Screening and enrolment of patients, Section 7.2 Delivery of the vector, Section 7.3.2. Hazards related to the AAV6 vector, Section 9. Study related investigations and follow-up, Section 12.3 Study funding, Section 12.4, Section 13.2 Data Collection and Section 14. Pharmacovigilance.

Protocol version 9 The following sections in the protocol have been updated. Abbreviations, Section 1. Investigators, Section 3. Background and Rationale, Section 4. Aims of the study, Section 5. Trial design, Section 6. Eligibility Criteria, Section 7. Randomisation, Section 8. Delivery of the IMP, Section 10. IMP composition, Section 12. Study related Investigations, Section 13. Outcome measures, Section 13. Scientific studies after LVAD insertion, Section 14. Statistics, Section 15.4 Study funding, Section 16. Regulatory Issues and Section 17. Expected Serious Adverse Events/clinical outcomes

Protocol version 10. Following advice from the Principal Investigators at each of the participating centres, additional exclusion criteria have been added to the protocol to account for patients that are at a high risk of left ventricular assist device (LVAD) thrombosis and the effect of altering or temporarily stopping anticoagulation prior to administration of the gene therapy. Weekly visits during the month after gene transfer have been amended to reduce the need for patients to travel to hospital so frequently. Visits in week 1 and 3 will be conducted as home visits by a trained member of the study team at each hospital and weeks 2 and 4 will remain as visits to hospital.

Protocol version 11 Protocol version 10 has been updated.

Protocol version 12 Reasons for amendment • Clarification regarding trial samples including size of myocardial tissue samples, transfer and analysis • Update to IMPD to include clarification regarding manufacturing process, updated information on packaging operations and QP release • Change to IMP labelling due to extension of expiry date • Minor amendments have been made to the protocol and patient information sheet to correct typographical errors and administrative details

The amendment is to temporarily halt recruitment to the trial . Results of the CUPID2 trial were announced by Celladon Corporation at the end of April in the form of a press release. Celladon Corporation is the IMP supplier for the SERCA-LVAD trial and the CUPID2 trial used the same IMP and administration protocol. The results of CUPID2 were negative, indicating that there is no evidence of benefit of AAV1/SERCA2a compared to placebo control. No safety concerns were raised for AAV1/SERCA2a (MYDICAR). The TSC advised a temporary halt to the trial as it is considered that the risk/benefit ratio is altered in light of the CUPID2 results.

The Investigators and Trial Steering Committee have decided the following: • Recruitment to the trial will not recommence • Trial assessments that do not introduce an additional risk to patients will continue for existing patients (only one patient out of five still requires their 6-month follow-up visit). This is considered to be important for safety, scientific and ethical reasons as this is a safety trial and the data could be important for the individual patients and the study in general. • The end of the trial will be declared after the final patient’s 6-month follow-up visit which is estimated to take place by the end of September