Using Northern blot analysis and radioimmunoassay, we measured atrial natriuretic polypeptide (ANP) messenger RNA and ANP levels in the ventricle in patients with old myocardial infarction and investigated the relationship between ventricular ANP synthesis and hemodynamic parameters. Levels of ANP messenger RNA and ANP were markedly increased in the left ventricular aneurysm, and a positive correlation was observed between the ANP level in the left ventricular aneurysm and pulmonary capillary wedge pressure (r = 0.85, p less than 0.05). These findings indicate that ANP synthesis in the ventricle is increased in accordance with the severity of congestive heart failure.