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Dilated cardiomyopathy (DCM), a heart muscle disease characterized by ventricular dilation and dysfunction, is a leading cause of mortality and morbidity. In the present paper we will consider the main results of studies on the natural history of DCM in 581 consecutive patients prospectively enrolled and systematically followed in the Heart Muscle Disease Registry of Trieste in the last 25 years. In the last decades prognosis of DCM significantly improved over time, mainly as a consequence of optimized treatment with ACE-inhibitors and beta-blockers. However, a strong heterogeneity of prognosis was observed among patients both in familial and sporadic cases. Early diagnosis and treatment allowed to recognize two distinct subgroups, one with a rapidly progressive downhill course, high mortality and urgent indication to heart transplantation, another with a more favorable outcome. Long-term optimized treatment with ACE-inhibitors (in 90% of cases) and beta-blockers (in 87% of cases) was associated with a remarkable clinical improvement in 50% of patients and apparent "healing" in 16% of cases. A systematic and accurate echocardiographic follow-up showed in these cases a significant improvement of the left ventricular ejection fraction (LVEF) with "reverse remodeling", frequently associated with a decrease of severity of functional mitral regurgitation and regression of the restrictive filling pattern. The response to optimal treatment showed a strong relation to long-term outcome. The 8-year transplant-free survival, starting from the evaluation at 2 years, was 31% in patients with persistent NYHA class III-IV, 64% in NYHA class I-II and LVEFor = 40%, 83% in NYHA class I-II and LVEF40% and 94% in patients with apparent "healing" (p0.0001). Long-term follow-up showed a significant clinical progression of the disease in 33% of cases, independently of the initial clinical response to treatment. Predictive factors of a favorable response to beta-blocker treatment associated with ACE-inhibitors were a history of mild hypertension, an early diagnosis and treatment and the presence of sinus tachycardia. The risk of sudden death was increased particularly in patients with long-term persistent or progressive left ventricular dilation and dysfunction. A rigorous pharmacological approach (optimization of beta-blockers, withdrawal or decrease of dosage of digitalis), and selective non-pharmacological strategy (automated implantable cardioverter-defibrillators for primary prevention in high-risk patients) are potentially effective to decrease the incidence of sudden death during long-term follow-up. In conclusion, the Heart Muscle Disease Registry of Trieste gave us in the last 25 years new insights into the natural history of DCM, underlying the importance of a rigorous and systematic approach both at clinical presentation and during long-term follow-up on optimized medical treatment.