In patients with supraventricular rhythm disorders ambulatory electro-cardiographic recording (Holter system) is an indispensable examination as it detects attacks that pass unrecorded by conventional ECG, being asymptomatic, too brief or too rare. It confirms the diagnosis, defines the factors triggering the attacks, detects the association of rhythm and conduction disorders, guides the treatment and monitors its effectiveness. Sequential ambulatory recording lends itself particularly well to this last objective. Biochemical examinations explain the cause of certain relapses (potassium depletion, high alcohol blood level) or detect the origin, clinically more or less obvious, of these disorders of rhythm (essays of thyroid hormones). Measuring blood levels of therapeutic drugs makes the handling of these various drugs safer. Finally, echocardiography detects an underlying heart disease, evaluates the size of the left atrium (a factor of relapse when it is dilated and of embolism when it harbours thrombi) and assesses the left ventricular function before administration of antiarrhythmics which, to varying extents, are all negative inotropic drugs.