To characterize the abnormal pattern of instantaneous left ventricular (LV) ejection in heart failure, proximal aortic pressure, flow, acceleration, power and dW/dt were measured at rest and during supine bicycle exercise using high-fidelity, catheter-mounted pressure and velocity sensors in 16 patients with idiopathic dilated cardiomyopathy (IDC) and 11 normal control subjects. In patients with IDC, peak flow was lower than normal both at rest (454 +/- 155 vs 649 +/- 168 ml/s, p less than 0.01) and during exercise (569 +/- 213 vs 916 +/- 329 ml/s, p less than 0.01). Peak acceleration, power and dW/dt were also significantly reduced in patients with IDC at rest and during exercise. Time to peak flow (as a fraction of LV ejection time) was consistently prolonged in patients with IDC (rest, 0.40 +/- 0.08 vs 0.29 +/- 0.04; exercise, 0.36 +/- 0.06 vs 0.28 +/- 0.04, both p less than 0.01). Exercise-induced increments in peak flow, power and dW/dt were significantly blunted in patients with IDC. Studies during pacing tachycardia and nitroprusside administration failed to reproduce the abnormalities during exercise in patients with IDC. Thus, the instantaneous flow pulse in heart failure is both diminished in magnitude (decreased stroke volume and peak flow) and abnormal in shape (decrease peak acceleration and delayed time to peak flow). Exercise stress in IDC results in abnormalities of LV performance that can be detected using instantaneous ejection information. These abnormalities are unlikely to be explained by changes in heart rate or loading conditions.