Unmitigated Aldosterone Signaling During Standard Clinical MRA Dosing

This study is investigating how well the standard dose of a drug called a mineralocorticoid receptor antagonist (MRA, such as spironolactone) actually blocks a hormone called aldosterone in people with stable chronic heart failure — because there's some evidence the standard dose may not be enough. **You may be eligible if...** - You have stable, chronic heart failure that is well-controlled (NYHA Class I or II) - Your kidney function is above a minimum threshold (eGFR over 30) - Your blood potassium is within the normal range (3.5–5.0 meq/L) - Your heart failure medications have been stable for several months - You have been free from a heart failure flare-up for at least 60 days **You may NOT be eligible if...** - You have uncontrolled high blood pressure (over 160 mmHg) - You have severe bladder problems - You are already on a high dose of spironolactone (over 50 mg) - You have a history of dangerously high potassium levels (over 6.0 meq/L) - You have a particularly unstable or complex form of heart failure - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.