Aims and methods To: (i) describe the baseline characteristics of patients in ATMOSPHERE and the changes in the planned analysis of ATMOSPHERE resulting from the mandated discontinuation of study treatment in patients with diabetes; (ii) compare the baseline characteristics of patients in ATMOSPHERE with those in the Prospective comparison of Angiotensin Receptor neprilysin inhibitors with Angiotensin converting enzyme inhibitors to Determine Impact on Global Mortality and morbidity in Heart Failure trial (PARADIGM-HF); and (iii) compare the characteristics of patients with and without diabetes at baseline in ATMOSPHERE. Results A total of 7063 patients were randomized into ATMOSPHERE April 2009-April 2014 at 755 sites in 43 countries. Their average age was 63 years and 78 were men. ATMOSPHERE patients were generally similar to those in PARADIGM-HF although fewer had diabetes, renal dysfunction, and were treated with a mineralocorticoid receptor antagonist. In ATMOSPHERE, patients with diabetes differed in numerous ways from those without. Patients with diabetes were older and had worse heart failure status but a similar left ventricular ejection fraction (mean 28 ); they had a higher body mass index and more co-morbidity, especially hypertension and coronary heart disease. Mean estimated glomerular filtration rate was slightly lower in those with diabetes compared with those without. Conclusion ATMOSPHERE will determine whether patients with HF and reduced ejection fraction (particularly those without diabetes) benefit from the addition of a direct renin inhibitor to standard background therapy, including an angiotensin-converting enzyme inhibitor, beta-blocker, and a mineralocorticoid receptor antagonist. ATMOSPHERE will also determine whether aliskiren alone is superior to, or at least non-inferior to, enalapril.