Swedish Cardiac And Renal Failure Study-1

Inclusion Criteria: * The participant has given their written consent to participate * A diagnosis of HFrEF according to current criteria, for at least three months before the screening visit * Echocardiography within 24 months of the screening visit with ejection fraction ≤ 40%. The responsible investigator is allowed to order a new TTE at their own discretion if clinically indicated - e.g. following the initiation of markedly intensified HFrEF-treatment or in the event of significant clinical deterioration. If the new TTE shows an EF \> 40%, the participant will not be eligible for inclusion. However, a potential echocardiographic worsening should not, by itself, preclude enrollment * New York Heart Association class II-III * Optimally treated and stable HFrEF (according to the investigator) since at least four weeks before the screening visit. Treatment should include beta-blockers, sodium/glucose co-transporter 2 inhibitors, angiotensin-converting enzyme inhibitors, or angiotensin receptor blockers if eGFR ≥ 20 ml/min/1.73m2 according to the revised Lund-Malmö method. Participants should also have cardiac resynchronization therapy or an implantable cardioverter-defibrillator if the indication exists according to current guidelines * eGFR \< 30 ml/min/1.73m2 according to the revised Lund-Malmö method at least once during the 12 months before the screening visit, and eGFR \< 45 ml/min/1.73m2 at the time of inclusion Exclusion Criteria: * P-K ≥ 5.6 * For the first ten study participants: eGFR \< 20 ml/min/1.73m2 according to the revised Lund-Malmö method, or projected decline in eGFR to \< 10 ml/min/1.73m2 during the 36-week study period. The projected decline will be estimated using the three most recent eGFR values from the previous 6-12 months \- For the remainder of the study participants: eGFR \< 10 ml/min/1.73m2 according to the revised Lund-Malmö method, or projected decline in eGFR to \< 10 ml/min/1.73m2 during the 36-week study period. The projected decline will be estimated using the three most recent eGFR values from the previous 6-12 months * Ongoing/planned dialysis * Systolic blood pressure \< 90 mmHg * Uncontrolled hypertension as judged by the investigator * Severe hepatic impairment (Child-Pugh C) * History of, or planned, heart transplantation or left ventricular assist device * Unwillingness to comply with highly effective contraceptive methods, or ongoing/planned pregnancy, or breastfeeding * Previous allergic reaction to an MRA or a potassium binder * Ongoing treatment with lithium, cyclosporine, tacrolimus, nonsteroidal anti-inflammatory drugs, trimethoprim, or strong CYP3A inhibitors (ketoconazole, itraconazole, ritonavir, nelfinavir, clarithromycin, telithromycin, and nefazodone) or inducers (rifampicin, carbamazepine, phenytoin, phenobarbital, and St. John's Wort) * QTc(f) ≥ 550 msec, history of QT prolongation associated with any medication requiring medication discontinuation, or congenital long QT syndrome * Uncontrolled arrhythmia as judged by the investigator * Acute cardiac hospitalization or procedure within four weeks before inclusion * Not suitable as judged by the investigator (presumed inability to participate, severe or terminal co-morbidity, and expected survival \< 12 months) * Previously enrolled in this trial or participation in another trial not approved for co-enrollment