Exercise echocardiography with image acquisition during treadmill exercise is the most common form of stress testing used in our department. The usual evaluation of patients with hypertrophic obstructive cardiomyopathy consists of serial echocardiographic studies at rest. The purpose of this study was to evaluate intraventricular gradients during exercise echocardiography in patients with a diagnosis of hypertrophic obstructive cardiomyopathy. We studied 13 patients, 8 male, mean age 56 +/- 9 years Intraventricular gradients were measured using continuous wave Doppler; two evaluations were performed at rest: one in left lateral decubitus and the other in orthostatic position after one minute in this position. The patients then underwent a treadmill exercise test using the modified Bruce protocol, during which intraventricular gradients were measured at peak exercise. Finally, a further measurement was taken in the first 90 seconds of the recovery period in left lateral decubitus. The intraventricular gradient in left lateral decubitus was 54 +/- 29 mmHg; in orthostatic position 69 +/- 30 mmHg (p < 0.001 versus gradient in left lateral decubitus); at peak exercise 109 +/- 47 mmHg (p < 0.001 versus gradient in orthostatic position); and during recovery in left lateral decubitus 78 +/- 33 mmHg (p < 0.001 versus gradient at peak exercise in orthostatic position). We conclude that intraventricular gradients increase significantly in orthostatic position and increase considerably during treadmill exercise testing. The gradients measured in the recovery period do not reflect what happens during effort or therefore during these patients' daily activities. This type of evaluation can help us to better understand the pathophysiology of patients with a diagnosis of hypertrophic obstructive cardiomyopathy and to optimize treatment.