Background: Dyspnoea is one of the most common symptoms in the emergency department, and identification of its cause may require complex diagnostic tests. In everyday practice, some concerns arise when the reported dyspnoea is not fully compatible with objective measures in additional tests. This study was performed to evaluate which objective diagnostic markers differentiate patients admitted to hospital due to acute heart failure with and without resting dyspnoea, with a special emphasis on haemodynamic parameters measured by impedance cardiography. Methods: This study enrolled patients over 18 years of age who were hospitalised due to acute heart failure. The admission evaluation included haemodynamic profiling by ICG, with special emphasis on parameters characterising afterload (systemic vascular resistance index), cardiac function (cardiac index; stroke index), and congestion (thoracic fluid content). Results: The study population consisted of 102 patients, mostly men (76.5%), with a mean age of 71.4 ± 12.5 years and a left ventricle ejection fraction of 37.3 ± 14.1%. Patients with dyspnoea at rest (n = 41), in comparison with those without this symptom (n = 61), presented with poorer clinical states: more frequent orthopnoea (p = 0.002), tachypnoea (p = 0.001), palpitations (p = 0.004), and peripheral hypoperfusion (p = 0.0005), higher concentration of high-sensitivity troponin T (p = 0.021), and higher thoracic fluid content (p = 0.003). No significant differences were noted for haemoglobin, creatinine, N-terminal pro-brain natriuretic peptide, heart rate, blood pressure, chest X-ray, left ventricular ejection fraction, cardiac index, stroke index, or systemic vascular resistance index. Conclusions: Thoracic fluid content assessed by impedance cardiography was found to be a good diagnostic marker for differentiating patients admitted to hospital due to acute heart failure with and without resting dyspnoea, and was superior to chest X-rays, N-terminal pro-brain natriuretic peptide, and left ventricle ejection fraction.