Two low noise electrocardiographic systems were designed to record low amplitude His-Purkinje potentials in the PR segment and delayed depolarization potentials in the ST-T segment from the body surface on a beat to beat basis. In one system, a bipolar electrode was utilized and the noise level was optimally reduced to 2 to 2.5 μV by a combination of noise reduction techniques. In the second system, better noise reduction (1 to 1.5 μV) was achieved by utilizing spatial averaging from 16 pairs of electrodes and a specially designed volume conductor electrode. The low noise electrocardiogram using the volume conductor electrode identified the His-Purkinje potential (up to 6 μV in amplitude) in 43% of patients compared with 71% recorded in the signal-averaged electrograms from the same patients. However, in contrast to the signal-averaged electrogram, only the low noise electrocardiogram could identify the His-Purkinje potential when moment to moment dynamic changes of the temporal relation of the P wave and QRS complex occurred. On the other hand, the low noise electrocardiogram recorded low amplitude, late diastolic potentials in the ST-T segment of postinfarction patients who showed a propensity to develop ventricular tachyarrhythmias. The diastolic potentials either: 1) remained constant in successive sinus beats, 2) varied in configuration, amplitude and timing in successive sinus beats, or 3) were only recorded in the diastolic interval preceding possible “reentrant” ventricular beats. The present study proves the feasibility of recording low amplitude His-Purkinje potentials and late diastolic potentials on the body surface on a beat to beat basis utilizing low noise electrocardiographic systems. Recording of late diastolic potentials on a beat to beat basis has the exciting potential of directly identifying malignant “reentrant” versus benign “focal” ventricular rhythms. However, the clinical relevance of these potentials remains to be established.