The components of the measuring instrument used for the present investigation are explained, and, using this second derivative gradiometer type SQUID magnetometer, studies on the fetal magnetocardiogram and on the magnetocardiogram in the normal controls and of patients with various cardiac diseases were carried out in a magnetically unshielded environ-ment. In these studies the simultaneous recordings of MCGs and ECGs were always taken at the same precordial chest position V₁ to V₆.
From the observation of MCGs in these studies, we obtained many more perspicuous informations useful for clinical diagnosis than from ECG. As to the MCGs in the patients with anterior myocardial infarction, we have observed 2 kinds of characteristic changes in MCGs pattern and this fact was demonstrated by an experiment using dogs. Further, in the MCGs from a patient with complete A-V block we have found a secondary atrio-ventricular pace-maker spike which might be related with the ventricular depolarization.