Heart failure with preserved ejection fraction (HFpEF) involves half of hospitalised patients with heart failure (HF), but estimates vary due to unclear diagnostic criteria. We performed a prospective observational study of hospitalised patients admitted with dyspnoea. The aim was to apply contemporary guidelines to diagnose HF due to valvular disease (HFvhd), HF due to reduced ejection fraction (HFrEF), HF due to midrange EF (HFmrEF) and HFpEF in relation to presumed cardiac or non-cardiac dyspnoea. Methods We included consecutive hospitalised patients with presumed HF or dyspnoea and excluded patients with acute coronary syndrome, estimated glomerular filtration rate <30 mL/min/1.73 m or low NT-proBNP (<296 ng/L). Higher age-adjusted NT-proBNP values excluded patients with presumptive non-cardiac dyspnoea. Contemporary criteria for HFpEF and diastolic dysfunction were assessed, and we adjudicated whether acute decompensated HF (ADHF) had been the primary diagnosis. Results Of 707 eligible patients, we included 370 patients of whom 75 had non-cardiac dyspnoea. Of these, 10% (38/370) had no cardiac dysfunction. Cardiac dysfunction consisted of 18.4%, HFvhd, 30.1% HFrEF, 10.2% HFmrEF and 41.3% HFpEF. HFpEF was twice as common in presumptive non-cardiac dyspnoea versus cardiac dyspnoea (71% vs 34%, p<0.0001). However, adjudicated ADHF was the primary diagnosis in 80% of HFrEF, 62% of HFmrEF and just 28% of HFpEF. Conclusion HF according to contemporary criteria applied to 90% of patients admitted with dyspnoea and elevated NT-proBNP irrespective of the presumptive cause of dyspnoea, of whom 10% had HFmrEF and 41% HFpEF. However, significant non-cardiac diagnoses related to 9 out of 10 with HFpEF with pulmonary disease as the predominant adjudicated problem.