Final answer:
Spironolactone improves heart failure symptoms and prolongs survival by blocking aldosterone receptors, thereby inhibiting sodium reabsorption and avoiding increased water retention without promoting potassium excretion.
Step-by-step explanation:
The potassium-sparing diuretic spironolactone (Aldactone) prolongs survival and improves heart failure symptoms primarily by blocking aldosterone receptors. Aldosterone is a hormone that increases water levels in the plasma by reducing the excretion of sodium. Spironolactone's antagonistic action at these receptors inhibits sodium reabsorption and water retention, mitigating the effects of heart failure. Unlike other diuretics, it does not promote the excretion of potassium, hence the designation as a potassium-sparing diuretic.