Percutaneous balloon mitral valvuloplasty (PBMV) has been shown to induce an immediate increase in the left ventricular end-diastolic volume, which increase, in turn, has been attributed to an increase in left ventricular compliance. We studied 51 patients, 41 women and 10 men, who underwent PBMV, and were in sinus rhythm before and after the procedure. Heart rate did not vary significantly. There were increases in left ventricular end-diastolic volume (97.5 +/- 25.6 vs 112.7 +/- 25.7 ml/m2, P < 0.001), left ventricular end-diastolic pressure (8.7 +/- 3.0 vs 9.7 +/- 4.3 mmHg, P = 0.04), and both left ventricular systolic pressure and stress (118 +/- 20.5 vs 123 +/- 23.2 mmHg and 468 +/- 129 vs 580 +/- 164 mmHg; P = 0.04 and P < 0.001, respectively). The elastic stiffness constant did not vary (16.2 +/- 1.9 vs 15.7 +/- 1.9 (dimensionless units), P = 0.2). The increase in volume seemed to be particularly important when the ventricle appeared to be "shrunken" before PBMV. This increase was still present after a 1 year follow up. Thus, PBMV determines an increase in both end-diastolic volume and pressure, so that the left ventricle appears to move along a single pressure-volume curve. This enlargement evokes the Frank Starling mechanism, and improves systolic performance. Since it is still evident after a 1 year follow up, some concern may arise when a simultaneous volume overload is present, as in aortic insufficiency.