The most important diagnostic tool available in assessment of dysfunction of the autonomic control of the heart is the clinical history which must be taken in the greatest possible detail including from the patient and witnesses of the syncope/event. Correct history taking will make many diagnoses avoiding need for further testing and guide further investigation if needed and when appropriate. This paper focusses on the investigation of patients when required, the available tests, their indications, how to perform them for maximum yield and how to interpret the results. Tilt-testing, carotid sinus massage, active stand, cardiovascular autonomic nervous system tests, ambulatory blood pressure and insertable ECG loop recorder are covered.