Four cardiac hormones i.e. atrial natriuretic peptide (ANP), vessel dilator, long acting natriuretic peptide (LANP) and kaliuretic peptide have anticancer effects in vitro. These four cardiac hormones were infused subcutaneously for 28 days with weekly fresh hormones at 3 nM min^-1 kg^-1 body weight in athymic mice bearing human breast adenocarcinomas. Vessel dilator, LANP, kaliuretic peptide and ANP eliminated 67%, 50%, 67% and 33% of the HTB-132 human breast adenocarcinomas. LANP eliminated 100% and vessel dilator 1/3 of CRL-2327 breast adenocarcinomas. There was no recurrence of the breast cancers in the primary site and no metastasis except in the ANP-treated group in one year post-treatment. The natriuretic peptide receptors-A and -C were decreased 50% and 31%, respectively, in metastatic versus primary ANP-treated breast adenocarcinomas. Four cardiac hormones eliminate up to two-thirds of human breast adenocarcinomas in athymic mice.