The Starling11 curve originally described the increased contractility of cardiac muscle fibres in response to increased stretch; it can be extrapolated to the whole ventricle to explain the normal relationship between filling pressure and ejection fraction (Fig. 24.4). Most patients with heart failure present in phase 'A' of the relationship, and before the ventricle is grossly dilated (the decompensated phase, 'B')- While diuretic therapy improves the congestive symptoms of cardiac failure which are due to the increased filling pressure (preload), it actually reduces cardiac output in most patients. Depending on whether their predominant symptom is dyspnoea (due to pulmonary venous congestion) or fatigue (due to reduced cardiac output), patients feel better or worse. It is likely that a principal benefit of using ACE inhibitors in cardiac failure is their diuretic sparing effect.
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