A portable apparatus for monitoring heart activity, including two electrodes connected to a case which encloses an electronic signal processor. The electrodes are separate and applied to different parts of the cardiac region of the patient's bust, one electrode being exposed on a face of the case to contact a first zone on the patient's bust, the other electrode being independent of the case and contacting a second zone of the bust, the electrodes being connected electrically by a conductor which also serves as a strap to suspend the apparatus on the patient's body.