Both theoretic considerations and actual studies suggest that spatial vectorcardiography will eventually have practical applications. It is likely to furnish clinically useful information in addition to that provided by conventional electrocardiography. This is a statement of probability, however, and has not yet been established, nor have the circumstances in which it may apply yet been defined. For this reason the current status of vectorcardiography is properly that of a research method, not yet suitable for general clinical application. Many technics have been employed to obtain the vectorcardiogram. The graphic derivation of vectorcardiograms from electrocardiographic leads is of historic interest only. The use of the cathode ray oscilloscope with suitable amplifiers is the method of choice. Many modifications of technic, such as recording on moving film, recording of successive complexes, and stereoscopic recording, are possible with the use of the cathode ray oscilloscope. It is not yet apparent which recording technic will prove to be most informative, so that studies with a variety of technics seem advisable. Several systems of electrode placement have been advocated for obtaining the spatial vectorcardiogram. Since the application of any geometric reference frame to the human body necessitates several assumptions which are not actually true, it appears that the choice among reference frames cannot be made on the basis of their intrinsic validity. We are of the opinion that the equilateral tetrahedron introduced by Wilson and associates 12 offers advantages over other reference frames because: (1) Only one electrode is necessary in addition to those employed to obtain the standard electrocardiographic leads. (2) Electrodes are easily applied, and their positions are readily reproducible. (3) The knowledge already available from experience with the standard leads of the electrocardiogram may be applied to spatial vectoreardiography. (4) Each of the four surfaces defined by the electrode positions is an equilateral triangle. (5) The disadvantages of this reference system are common to those of other proposed reference frames. Variations of the spatial vectorcardiogram in normal man and in man with a variety of disease states have been studied by several groups of investigators with a variety of technics. These studies are of considerable importance, but as yet nearly all lack pathologic confirmation of the presence, site and size of suspected lesions. These data must be obtained and thoroughly correlated with the vectorcardiogram before vectorcardiography can be employed with certainty in general clinical practice.