Abstract: The study of electrocardiograph signals (ECG) in the time or in the frequency domain taken separately doesn't allow the detection of arrhythmia and late potentials. The second order Choi Wigner Ville transformation can be applied for the detection of cardiac late potentials, and the problem of how to remove cross-terms is analyzed. The method is effective, especially for real non Gaussian signal. It gives better time frequency resolution and provides doctor with a tool for diagnosis.