I N DETERMINING the cardiovascular effects of drugs, the need for a convenient clinical method has led several investigators to the use of ballistocardiograph)I.‘-4 Most of these investigations have been concerned primarily with the drug-elicited changes in cardiac output as measured I))I the ballistocardiograph. However, Hamilton et al.” concluded that the amplitude of the ballistocardiogram was more closel!related to the velocityof ejection than to the quantity of blood ejected. Starr and others related the amplitude and contour of the ballistocardiographic complexes to the rate of application of simulated heart force in cadavers6-8 In addition, several investigators have shown that hallistocardiographic amplitude is greatly reduced but not completely eliminated by occluding the venous return to the heart or by preventing the ejection of blood by the heart. These investigators have concluded that the amplitude of the ballistocardiogram is largely determined I)v the forces involved in the movement of blood. !‘-11 Several methods have evolved for obtaining records of the l)ody movements occurring with each heart beat. NotalA)-, these arc the Starr table (a high-frequency system), the ultra-lowfrequency system, and the direct-hod>method. The physics of these systems and the artcfacts in their records have been descril,cd”-I4 and have been discussed also bv others in this Seminar. However, for the purpose of cI,aluating the acute influence of drugs on the human cardiovascular system some of the advanta,ges of the direct-bed\method might I)e pointed out here: (1) Directbody recordings are easily obtained without discomfort to the subject. (2) They may t)c ohtained from the patient confined to the hospital t)cd. (3) The low cost of installation of the equipment permits the use of direct-body units in the physician’s office. Based on the above considerations, studies were instituted in this laborator)to investigate the applicabilit\of t>allistocardiography as a clinical method of e\,aluating acute drug-produced changes in rn)-ocardial contractilit)-.i5-‘$’ The general plan of thcsc investigations has I)een