To evaluate the transcardiac extraction of aldosterone before and after spironolactone administration to patients with congestive heart failure, we measured the plasma aldosterone in the aortic root and the coronary sinus in eight congestive heart failure patients with dilated cardiomyopathy. The plasma aldosterone level was significantly lower in the coronary sinus than in the aortic root before spironolactone administration (87.5 +/- 16 versus 62.2 +/- 11 pg/ml, p = 0.01). After chronic treatment with spironolactone, there was no significant difference in the aldosterone level between the aortic root and the coronary sinus (151 +/- 49 versus 148 +/- 48 pg/ml), and the transcardiac gradient of aldosterone (aortic root to coronary sinus) was significantly decreased (25.3 +/- 7.3 versus 3.1 +/- 4.5 pg/ml, p = 0.046). These results indicate that plasma aldosterone is extracted through the heart in congestive heart failure patients with dilated cardiomyopathy, and that spironolactone inhibits the transcardiac extraction of aldosterone in congestive heart failure patients. This suggests that spironolactone blocks the effects of aldosterone on the failing heart in congestive heart failure patients with dilated cardiomyopathy.