Background: The efficacy and safety of angiotensin receptor neprilysin inhibitor (ARNI) for patients with an estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73m2 have not been established. This paper reports three cases of low eGFR wherein ARNI was effective against heart failure and high blood pressure. Case: In case 1 (a woman in her 70 s), eculizumab was used to treat chronic kidney disease (CKD) because of an atypical hemolytic uremic syndrome. Surgery was performed for the exacerbation of chronic heart failure due to worsening mitral regurgitation. The postoperative course was stable. However, from the third disease day, her kidney failure exacerbated (eGFR decline from 16 to 10 mL/min/1.73 m2), heart failure flared up again (B-type natriuretic peptide [BNP] elevated from 500 to 1200 pg/mL), hemodialysis was performed, carperitide was added, and the diuretic stage was started. However, the drug could not be discontinued, and ARNI was initiated (50 mg once twice a day). Consequently, the eGFR was recovered (elevated from 10 to 18 mL/min/1.73 m2), the urine output was increased, and the heart failure was recovered (BNP declined from 1200 to 250 pg/mL). In case 2 (a man in his 80 s), CKD exacerbation due to diabetic nephropathy (eGFR of 18 mL/min/1.73 m2) led to heart failure, and hemodialysis therapy and ARNI (50 mg once two times a day) were initiated. Good diuresis became available, and hemodialysis could be withdrawn (BNP declined from 120 to 70 pg/mL, and the bodyweight from 95 to 75 kg). Since then, the urine output has been maintained, and peritoneal dialysis has been initiated and continued. In case 3 (a man in his 70 s), in whom 6 months had elapsed since the initiation of hemodialysis therapy for CKD caused by diabetic nephropathy, the dry weight was appropriate, but the blood pressure tended to increase (from 140/80 to 186/96 mmHg). Moreover, BNP levels had increased (BNP elevation from 70 to 180 pg/mL). When telmisartan 40 mg once a day was changed to ARNI (100 mg once a day) as an antihypertensive agent, the blood pressure was stabilized (from 186/96 to 140/80 mmHg), and the BNP decreased (BNP declined from 180 to 20 pg/mL). No adverse events were observed in all three cases. Discussion: These cases suggest that ARNI not only has diuretic effects but decreases blood pressure and BNP in patients with CKD, including those requiring dialysis. ARNI may be used relatively safely even in patients with reduced kidney function.