INTRODUCTION
Emotional disturbances may have a profound effect on the circulation, causing changes in the heart rate, cardiac output (1 and 2), blood pressure, tone of peripheral vessels, and the electrocardiogram (3). This is particularly true of the emotional state which may develop in persons who find themselves in a hazardous situation. For present purposes this emotional state is termed "anxiety," although it is recognized that other reactions such as resentment or anger may also occur, depending upon the individual and the circumstances. In any study on unanesthetized human subjects, changes produced by anxiety may mask completely the physiologic or pharmacologic effects which are obvious in a relaxed subject. In the interpretation of experimental data. objective criteria by which it can be established, or even suspected, that anxiety is having an effect on cardiovascular function are useful. It is also of importance to clinical medicine to have further information concerning