Abstract The vectorcardiographic appearance of the highly magnified T loop of 80 patients with arteriosclerotic heart disease was studied and compared with that of 20 normal subjects. The severity of the arteriosclerotic heart disease was evaluated by coronary arteriography. The following indicators were found to be characteristic of the subjects with arteriosclerotic heart disease and were considered to be abnormal: 1. 1. The T loop angle was outside the normal range in about half the cases, and was projected in a direction other than anterior, inferior and to the left in 50 per cent. 2. 2. A wide QRS-T angle was found in the frontal and horizontal planes in about half of the cases. 3. 3. A length/width ratio of 3.0 or less, considered abnormal in our study, was found in 39 per cent of the cases. 4. 4. Open T loops were found in the frontal plane in 36 per cent, in the horizontal plane in 47 per cent, and in the sagittal plane in 35 per cent. 5. 5. Terminal delay in the inscription of the T loop was considered abnormal and was noted in 41 per cent of the cases of arteriosclerotic heart disease. The rotation of the T loop and its relation to the rotation of the QRS loop appeared to have no significance in the diagnosis of arteriosclerotic heart disease.