Purpose To explore the use of neuroendocrine monitoring for more timely diagnosis of dilated cardiomyopathy (DCM) in Duchenne’s muscular dystrophy (DMD) and to determine the effects of angiotensin-converting enzyme inhibitors (ACEI) and β-blockers on neuroendocrine levels, left ventricular diastolic diameter (LVDd), ejection fraction, and mortality rate on DMD. Methods Eighty-five patients with DMD underwent yearly cardiac monitoring including neuroendocrine screening. Eleven patients had symptoms of DCM develop once plasma neuroendocrine levels increased. At this point the patients received ACEI for 9 to 62 months (35.8 ± 18.4 months) and β-blockers for 7 to 60 months (31.6 ± 20.1 months). Results The combination of ACEI and β-blockers relieved symptoms and signs of heart failure in all 11 patients and significantly reduced atrial natriuretic protein (ANP) levels from 197.5 ± 152.1 pg/mL to 25.5 ± 16.2 pg/mL ( P < .002) at 15.5 ± 8.2 months, brain natriuretic protein from 523.8 ± 434.8 pg/mL to 59.3 ± 24.2 pg/mL ( P < .05) at 12.2 ± 3.1 months (data complete for 5 patients), norepinephrine levels from 1114 ± 689 pg/mL to 360 ± 257 pg/mL at 20.5 ± 9.6 months for 11 patients (P = .001), and LVDd from 65.9 ± 9.2 mm to 63.3 ± 6.3 mm (P = .15) at 15.0 ± 7.4 months for 10 patients, including 3 for whom the LVDd increased by 2 to 6 mm. The combination increased left ventricular ejection fraction (LVEF) from 25.1% ± 9.2% to 36.5% ± 5.8% (P < .001) at 17.1 ± 11.0 months for 10 patients. For 9 of the patients ANP levels remained lower throughout the 36.8 ± 20.1 month course of the follow-up. Two patients had sudden severe re-elevations of ANP levels just before death from congestive heart failure after 44 and 23 months of therapy, respectively. Conclusion Neuroendocrine level monitoring can assist in the diagnosis of DCM in patients with DMD. Combination therapy with ACEI and β-blockers can significantly decrease neuroendocrine activation and LVDd and reverse symptoms and signs of congestive heart failure for patients with DMD. (Am Heart J 1999;137:895-902.)