Vectorcardiograms obtained with the Frank lead system were recorded in 258 healthy subjects (139 men, 119 women) and were classified according to QRS loop patterns. Sex and age effects on the vectorcardiograms were studied. We classified the vectorcardiograms into 4 types according to the frontal axis of the maximum QRS vector (A≧60>B≧30>C≧10>D). Type B was frequent among young persons and the number of persons with type C increased with aging. The magnitude of the maximum QRS vector diminished with aging in both sexes. The axis deviated horizontally and posteriorly in men and horizontally in women. The magnitude of the maximum T vector was larger in men than in women. The axis was more anterior in men than in women. The axis of the 20-msec QRS vector deviated from the right anterior to the left anterior. The terminal QRS vector demonstrated no sex or age defference. The percentage of the QRS Bite increased with aging.