A Study of AZD4063 in PLN R14del Dilated Cardiomyopathy

Inclusion Criteria: * Participants must be 18 to 80 years of age inclusive, at the time of Screening * Participants with pre-existing positive screening for R14 del PLN mutation * Participants with screening Left ventricular eject fraction ≤ 45% as assessed by echocardiography * Participants with New York Heart Association (NYHA) function class I-III * Participants on stable medical therapy for at least 6 weeks prior to Screening and during the Screening period, with no significant improvement in heart failure * Participants with implantable cardioverter-defibrillator (ICD) or Cardiac resynchronization therapy device (CRT-D) * Participants with Body mass index (BMI) within the range 18-35 kg/m2 * Females of childbearing potential must not be lactating, and if heterosexually active must agree to use an approved method of highly effective contraception * All women of childbearing potential must have a negative pregnancy test at the Screening Visit. Exclusion Criteria: * Participants with positive hepatitis C antibody, hepatitis B virus surface antigen or hepatitis B virus core antibody * Known to have tested positive for Human immunodeficiency virus (HIV) * Any known genetic mutation associated with hereditary electrical or structural disease * Congenital long QT syndrome * QTcF \< 350 ms * Known Short QT syndrome (SQTS) or family history of SQTS * Catecholaminergic polymorphic ventricular tachycardia (CPVT as calcium ion channelopathy) and recent hospitalization for heart failure or significant ventricular arrhythmia within 3 months * Participants with sustained ventricular arrhythmia requiring treatment and considered clinically not stable by the Investigator * History of subendocardial Late Gadolinium Enhancement (LGE) suggestive of previous myocardial infarction and/or significant coronary artery disease (50% \> stenosis in one major epicardial coronary artery or need for previous percutaneous coronary intervention or coronary artery bypass grafting) * Routinely scheduled outpatient intravenous infusions for heart failure * Uncontrolled hypertension * Significant primary valvular disease * Congenital heart disease * Left ventricular wall thickness of \> 13 mm or with any relative with hypertrophic cardiomyopathy (HCM) * Recent acute presentation of myocarditis * Restrictive or peripartum cardiomyopathy; infiltrative disorders (sarcoidosis) * Alcohol consumption in excess * Any laboratory values with the following deviations: 1. Alanine Transaminase \>2 upper normal limit (ULN) 2. Aspartate Transaminase \>2 ULN 3. Total bilirubin \> 2 x ULN 4. Estimated GFR \< 30 mL/min/1.73 m2 5. Hemoglobin \<10g/dL * Any vital sign values with the following deviations at Screening 1. Systolic blood pressure \> 160 mmHg 2. Diastolic blood pressure \> 100 mmHg 3. Pulse rate \> 100 beats per minute * Toxin exposure, systemic disease known to cause Dilated Cardiomyopathy (DCM) * History of severe allergy/hypersensitivity or ongoing clinically important allergy/hypersensitivity * Any history of cardiotoxic drug exposure with documented cardiomyopathy * Noncardiac condition that limits expected lifespan to less than 1 year * Participation in another clinical study with a study intervention administered in the last 3 months * Participants with a known hypersensitivity to AZD4063 * Participants who have previously received AZD4063 as part of this study * Participants who are part of a gene therapy trial