The rest and exercise hemodynamics in children with congenital valvar aortic stenosis were studied before and after aortic valvotomy. Eighteen patients were studied at rest; ten of the 18 patients were also studied during supine leg exercise using a bicycle ergometer. Aortic valvotomy resulted in a significant reduction in the mean left ventricular-aortic pressure gradient and in peak left ventricular systolic pressure with an increase in aortic valve area in most patients. There was an associated increase in the subendocardial blood flow assessed indirectly by the DPTI × O2c SPTI ratio. There was a minor increase in the degree of aortic insufficiency in most patients. Although, in general, there was significant hemodynamic improvement, three of the 18 patients still had significant residual stenosis after surgery and another four patients had a major increase in aortic insufficiency. The three patients with residual obstruction and one of the four patients with moderate to severe aortic insufficiency still had a DPTI × O2c SPTI ratio of less than 10, suggesting possible residual subendocardial ischemia. Also, the increased left ventricular end-diastolic pressures (LVEDP) present in nearly 50% of the patients before surgery did not change significantly after surgery. Three patients showed an actual increase in LVEDP after surgery. Before surgery, the left ventricular systolic pressure and mean gradient increased on exercise, but this increase was proportionately less than the increase in cardiac output, so that calculated aortic valve area increased on exercise. The DPTI × O2c SPTI ratio decreased significantly on exercise, suggesting an increase in myocardial ischemia. Successful surgery resulted in a reduction in left ventricular systolic pressure and mean left ventricular-aortic gradient on exercise, and in improvement in the subendocardial blood flow as assessed by the DPTI × O2c SPTI ratio. In general, children with severe aortic stenosis have relatively normal cardiac function on exercise. Some children did show a reduction of stroke index on exercise in spite of rising LVEDP. However, stroke work index increased in all of our children. Adult studies have shown many patients with decrease in stroke work index relative to LVEDP on exercise. The results of pre- and postoperative rest and exercise hemodynamics may be useful in evaluating results of surgery; the postoperative hemodynamic evaluation including the use of DPTI × O2c SPTI ratio provides additional useful information which can be used in making decisions concerning exercise activity after surgery.