Abstract: An apparatus for teaching electro-cardiography and vector-cardiography comprises, in its preferred form, a portable box having a first mirror attached to the box body and a second mirror attached to the inside of the lid so as to be normal to the first mirror when the lid is open. The first and second mirrors are marked to indicate the electrode leads on a patient in the horizontal and frontal planes, respectively. Between the mirrors is a loop-mounting means for mounting therebetween one of a series of vector-cardiographic loops representative of normal and pathological heart conditions. Orthogonal projections of any particular loop are reflected by the mirrors and such reflections can be used to assist in teaching electro-cardiography. A third Sagittal plane mirror may also be mounted, when the box is open, in orthogonal relation to the first and second mirrors for the teaching of vector-cardiography.