The association between the presence of areas of myocardial fibrosis and the appearance of unexpected DEVIATIONS OF THE QRS loop-outline on the vectorcardiographic tracing (bites) has been reported. In order to re-evaluate the correlation between the presence of bites and the possible existence of scars we have studied 511 patients. On the basis of clinical data, laboratory data, rest and exercise electrocardiograms, the subjects have been divided into four groups; 195 normal subjects; 267 with ischemic heart disease, 16 with arterial hypertension and 33 with diabetes mellitus (the last two groups as representative of subjects with higher risk for myocardial ischemia). Bites in at least one plane were detected in 9.7% of normal subjects, 27.8% of ischemic patients, 56.3% of hypertensive patients and 18.2% of diabetics (less than 0.001). The genesis of bites and reliability of the diagnostic criteria are discussed. With more restrictive criteria the frequency in the normal subjects falls to 1%, while in the other three groups it remains much higher (10.1%-12.5%-6.1%).