Doppler echocardiographic evaluation of the prosthetic valve function is usually performed at rest, although this situation is not representative for patients' daily activities. Therefore, a symptom-limited Master 2-step test was performed in 61 asymptomatic patients with normal left ventricular function. No adequate Doppler signals were obtained in 5 of 61 patients (8%) within 60 second after termination of exercise. In patients with aortic valve prostheses (n = 24), heart rate increased from 74 +/- 10 to 105 +/- 18 beats/min, the maximal instantaneous gradient from 44 (range 22 to 90) to 68 (range 28 to 165) mm Hg (r = 0.89) and the mean gradient from 24 (range 12 to 50) to 39 (range 18 to 100) mm Hg (r = 0.90). In 6 of 11 patients with a maximal flow velocity ratio between the left ventricular outflow tract and the aortic valve prosthesis less than or equal to 0.25, the mean gradient increased to a value greater than or equal to 50 mm Hg after exercise, whereas in patients with a ratio of greater than or equal to 0.25, this never occurred. In patients with mitral valve prostheses (n = 39), heart rate increased from 80 +/- 12 to 116 +/- 14 beats/min and mean gradient from 6 (range 3 to 10) to 14 (range 6 to 25) mm Hg (r = 0.59). The correlation of the mean diastolic pressure gradient after exercise with pressure half-time was 0.66. Systolic pulmonary artery pressure at rest and after exercise could be determined in 22 of 39 patients (56%) and increased from 34 (range 20 to 70) to 57 (range 35 to 110) mm Hg. It is concluded that the response to exercise can, to a large extent, be inferred from Doppler parameters at rest, particularly in patients with aortic valve prostheses. The clinical implication of the high gradients found in some asymptomatic patients in the present study should be elucidated by follow-up studies.