Reports on the implication of atrial natriuretic factor (ANF) for cardiac pacing and electrophysiology. Aspects of the diverse biological actions of ANF at the cellular and whole animal level; Role of ANF in modulating or causing pacemaker syndrome or altering the sympathetic response to atrial and ventricular arrhythmia; Development of specific and effect ANF inhibitors that would allow clarification of its role in producing symptoms in patients intolerant to ventricular pacing.