Cardiomyopathy is subdivided into dilated, hypertrophic, restrictive and isolated right ventricular type. Restrictive cardiomyopathy forms an important cause of diastolic dysfunction and heart failure with stiff myocardium in the presence of normal or increased ventricular wall thickness. Restrictive cardiomyopathy is characterized by dilatation of both atria in the presence of normal size or small sized ventricles and normal pericardium. This chapter covers the types of restrictive cardiomyopathy, hemodynamics of restrictive physiology, differentiation from constrictive pericarditis, cardiac amyloidosis, sarcoidosis, eosinophilic endomyocardial disease, and idiopathic (primary) restrictive cardiomyopathy. Mediastinal radiotherapy for the treatment of malignancies can result in spectrum of cardiovascular complications. These include pericarditis, myocardial fibrosis, muscular dysfunction, valvular abnormalities, and conduction disturbances.