From the literature concerning the electrocardiological diagnosis of myocardial infarction, data are reviewed illustrating the role of the scalar orthogonal approach by the Frank system. Special attention is drawn to the Q/R ratio as a parameter. Criteria for the most frequent differential diagnoses are summarized in a practical way. The importance of the concepts sensitivity and specificity is stressed, while statistical methods for establishing the value of parameters are discussed. Results of multivariate analysis are indicated.