**1. Introduction**

Dilated cardiomyopathy (DCM) is one of the most common cardiomyopathies causing heart failure (HF) worldwide. Although it is less common than coronary artery disease (CAD), it affects mainly young adults and presents the most frequent reason for cardiac transplantation in young age [1, 2]. According to the European Society of Cardiology (ESC), the current definition of DCM includes the presence of a dilated and poorly functioning left ventricle or of both ventricles [3]. A heterogeneous group of myocardial and systemic conditions may cause left ventricular dilatation in combination with dysfunction. In fact, identifying the etiology of DCM can be very challenging, which often leads to the common terminology of idiopathic dilated cardiomyopathy (IDC). Furthermore, DCM has a highly variable clinical presentation. While signs and symptoms of HF are most common, some patients are incidentally, for instance, by diagnosing cardiomegaly in chest X-ray. Other symptoms include arrhythmias, conduction disturbances, thromboembolic complications, or sudden cardiac death (SCD). In the last decades, major advances have been made in the understanding of molecular and genetic issues, as well as in the pathophysiology and clinical assessment of cardiomyopathies. Especially, understanding the genetic basis of DCM has improved considerably with the availability of genetic analysis. In addition, other important diagnostic approaches, particularly imaging methods are more widely available. This allows early diagnosis

and the initiation of adequate therapy, which already has led to an improvement of the prognosis in the last years. Data have shown that approximately 25% of DCM patients with recent onset of HF (<6 months) have ameliorated in symptoms or even have complete cardiac function recovery [4, 5]. However, the overall prognosis in patients with symptomatic HF and DCM is still poor. In order to further improve the prognosis of our patients, it is important to regularly gather the knowledge about the current state of DCM and adapt the appropriate diagnostic workups. Therefore, this chapter provides the reader with a comprehensive overview of the current state of DCM from definition over etiology including the genetics aspects to management for cardiovascular specialists.
