Impairment of relaxation and diastole is usual if not constant in cardiomyopathies and accompanies a disorder of cardiac contractile function. Certain heart diseases, especially hypertrophic cardiomyopathy, are associated with relative preservation of contractility and the predominant disorder concerns left ventricular filling. The clinical consequence of this impairment is dyspnoea due to elevated pressures of the left-sided cavities. The loss of atrial systole atrial is usually very poorly tolerated. There is an ambiguity of definitions, as, for the clinician, diastole starts at the time of closure of the aortic valve and consists of four phases: isometric relaxation, rapid ventricular filling, diastasis and atrial systole. In reality, this definition must be reviewed in physiological terms, asthe relaxation which allows the ventricle to return to its initial precontraction configuration is an active phenomenon which is actually part of ventricular systole. The reference methods of investigation remain haemodynamic methods with invasive measurements of left ventricular pressures and volumes. Myocardial isotope scan and especially echocardiography allow assessment of relaxation and diastole, although certain limitations of interpretation must be kept in mind. In terms of treatment, the demonstration of impairment of relaxation and diastole may require a different approach when contractile function is preserved. Calcium channel blockers could be useful and the preservation of atrial systole is always decisive.