A vectorcardiogram (VCG) was recorded in 22 patients in the acute phase of a right ventricular infarct in order to investigate any characteristic signs of this diagnosis. The RV infarct had been proven by at least two investigations: 2D echo, isotopes and right ventricular catheterisation. 17 patients had ST depression in V4R. The QRS complex presented two features: there was a reduced refractory period in every case, associated with septal extension in 3 cases and true posterior infarction in 11 cases, and, in the frontal plane, the QRS which was in clockwise rotation had showed an abnormal left axial lead in 18 cases with a maximal vectorial axis of between - 10 degrees and - 60 degrees. These modifications are similar to those seen in experimental infarcts of the RV. In conclusion, repeated VCGs in the acute phase of inferior infarction should suggest the diagnosis of right ventricular extension if it shows the appearance of more marked left axis deviation than that seen with isolated inferior infarcts. However, this sign is no constant and is not specific.