The diagnosis of primary dilated cardiomyopathy depends on the recognition of a dilated poorly contracting left ventricle with increased end-diastolic and end-systolic volumes in the absence of a detectable cause. The diagnosis is made only after exclusion both of structural heart disease and of known causes of secondary heart muscle disorder. The natural history is still largely unknown and is probably as variable as the likely causes. The left ventricular disorder does not cause symptoms until heart failure supervenes except for occasional patients who develop an early atrial or ventricular dysrhythmia, conduction defect, chest pain or murmur of mitral regurgitation. This period of latency may be short, prolonged or even permanent since it is unlikely that all cases progess to the point of failure. A few patients recover normal or near-normal cardiac function. The interplay between high blood pressure, hypertensive heart failure and dilated cardiomyopathy is illustrated by patients who recover from heart failure to become hypertensive and vice versa and in current treatment with vasodilators and diuretics for patients at either end of the spectrum.