Introduction: Acute heart failure is an increasingly common cause for hospital admissions. It is largely presumed that these patients have breathlessness at rest. In clinical practice, treatment for acutely breathless patients is usually given within minutes of presentation. Methods: We collected detailed information retrospectively from the case-notes of a representative sample of patients admitted with a primary death/discharge diagnosis of heart failure to determine what proportions of patients were Short Of Breath At Rest (SOBR) and Comfortable At Rest but Breathless On Slight Exertion (BOSE). We measured blood pressure (BP), heart rate and respiratory rate (RR) at initial presentation at 1, 2, 3, 4 – 6, 6 – 12 and 12 – 24 h. Results are described in median and Interquartile (IQR) ranges and the proportion with a systolic BP (SBP) > 125 mm Hg. We assessed mortality in different groups at discharge, and 30 days and 90 days after presentation. Results: Of the 100 patients enrolled, 46% had SOBR and 54% BOSE; 37% were women, the median age was 74 (IQR 68-84) years. Compared to patients with BOSE, patients with SOBAR had higher HR (105 vs 85 bpm), SBP (145 vs 120 mm Hg) and RR (25 vs 18 rpm). SBP (122 – 116 mm Hg), HR (85 –82 bpm), and RR (18 – 18 rpm) changed little amongst patients with BOSE in the first 4–6 h, but all declined steeply in patients with SOBR (141 –128 mm Hg, 100 – 90 bpm, and 24 – 20 rpm, respectively). After adjusting for age and sex, patients with BOSE had higher all cause mortality than SOBR (HR = 1.70, p = 0.002). Further adjustment with SBP, HR, RR, creatinine levels and LVSD provided more evidence that BOSE was independently predictive of all-cause mortality (HR = 2.20, p = 0.002). Conclusions: Most patients admitted with a primary diagnosis of heart failure present with BOSE rather than SOBR. Patients presenting with SOBR had, as expected, higher BP, heart and respiratory rates. BOSE showed little variation in these clinical characteristics in first 24h, but suffered higher mortality during hospital admission and at 30 and 90 days of presentation.