OBJECTIVE: To evaluate by echocardiography the cardiac structure and function in patients with primary adrenocortical insufficiency. DESIGN AND METHODS: Two-dimensionally guided M-mode echocardiograms and spectral Doppler studies were performed in seven consecutive patients with newly diagnosed autoimmune primary adrenal failure before and 4-8 months after an adequate regimen of steroid substitution. Echocardiographic parameters were also studied in ten healthy controls. RESULTS: In the cases with untreated Addison's disease, both left ventricular end-systolic and end-diastolic dimensions were significantly reduced in comparison with those in controls (P<0.01). Four patients had echocardiographic signs of mitral valve prolapse (MVP) at the anterior leaflet, with no evidence of mitral regurgitation by Doppler echocardiography. Systolic clicks characteristic of MVP were present on auscultation in two of these cases. Left ventricular chamber size normalized, i.e. significantly increased (P<0.01), and both echocardiographic and physical signs of MVP resolved after steroid substitution in all patients. All other echocardiographic indices were normal before and after treatment. CONCLUSIONS: Patients with untreated Addison's disease have cardiac abnormalities which regress after steroid substitution. A valvular-ventricular disproportion due to the hypovolemic state could explain these findings.