Right and left cardiac catheterization was performed in a 29-year-old male with dilated cardiomyopathy. During the procedure, prominent v waves appeared spontaneously in the pulmonary capillary wedge pressure recording with a simultaneous decrease in left ventricular systolic pressure. Left ventricular angiography showed moderate to severe mitral regurgitation and an ejection fraction of 22%. The right ventricular endomyocardial biopsy revealed histological findings consistent with dilated cardiomyopathy. Cardiac catheterization was repeated 9 months later, after a period of clinical improvement and a reduction in the right and left ventricular filling pressures was documented. The cyclic swings in the pulmonary capillary wedge pressure and in the left ventricular systolic pressure were not observed. Left ventriculography showed mild mitral regurgitation with an ejection fraction of 37%. Right ventricular endomyocardial biopsy documented a reduction in myofibrillar and nuclear hypertrophy. Thus, cyclic changes in pulmonary wedge v waves may be observed in dilated cardiomyopathy. This finding is consistent with cyclic variations in the degree of mitral regurgitation. Disappearance of this factor seems to be related to improvement in left ventricular contractility.