Abstract Two hundred patients undergoing cardiac catheterization were compared to determine the positioning of the tip of the central catheter. Two methods were compared: (1) the more traditional method uses roentgenograms, injecting the contrast medium in the lumen of the catheter; (2) the other method, less well known, directly guides the catheter using unipolar electrocardiogram (ECG). We demonstrated that both methods were accurate: in only four (2%) cases did the ECG method fail due to technical error; with the roentgenographic method, only one case failed to accurately position the tip of the catheter. Only the ECG method could demonstrate injury potential, that is, whether the tip of the catheter was too close to the right atrium or ventricular wall. This situation occurred in 39 of 200 (19.5%) cases.