This Series consists of ten drawers of a Kardex index, each of which is approximately 52 cm long. The top five drawers consist of indexed conditions, each of which is identified by a two or three character alphanumeric code (either A1 to A45, B1 to B99, or C1 to C70). Attached to each condition in the index is a list of the electrocardiogram numbers of particular patients. Dr. Segall seems to have determined that the listed electrocardiograms represent manifestations of their corresponding Kardex index condition. The individual electrocardiograms are located in Series G and are marked with their electrocardiogram numbers, the date on which they were created, as well as the names of the patients from which they were taken.

Drawers 6 through 10 of the Kardex index (Series M) contain indexed sections for 80 different cardiac symptoms. Each of the 80 symptoms are further divided into 10 (numbered 0 to 9) different sub-sections (possibly for different variations of each symptom), each of which contains a list of the electrocardiogram numbers, often, but not always, including the numbers for electrocardiograms of the patients whose files bear that particular two to three digit numerical code. The listed electrocardiograms seem to have been determined by Dr. Segall to represent manifestations of the corresponding Kardex index symptom.