Primary myocardial disease represents a pathologic process predominantly involving the heart muscle. Of 216 patients studied pertinent features were those of congestive heart failure, varying from mild to severe; arrhythmias, chest pain, and emboli were also noted. Cardiomegaly was present in the majority, although some had only some to moderate cardiac enlargement. Auscultation was of great importance in diagnosis. Gallop rhythm was one of the more frequent findings with atrial or ventricular gallops, or both, being present in the great majority. Manifestations of arrhythmias and /or conduction disturbances were common, as were systolic murmurs, particularly those of mitral and tricuspid insufficiency. Premature ventricular contractions, non-specific ST and T wave changes, arrhythmias and conduction disturbances represented the most common findings of the electrocardiogram. Primary myocardial disease represents a broad spectrum in regard to pathology, symptoms and signs, course and prognosis. Treatment consists of prolonged rest, management of congestive heart failure (including digitalization, Na restriction, and diuretics), and specific treatment of arrhythmias. Although generally not effective, steroids and anticoagulants appeared of benefit in selected cases. When a definite infection is present appropriate antibiotics are indicated; also, elimination of any toxic agent involved, or avoidance of alcohol in case of any alcoholic cardiopathy. Treatment must be focused on early diagnosis and appropriate prompt treatment, which theoretically, may determine whether the myocardial involvement can be arrested, reversed, or cured.