The advent of improved balloon catheters for percutaneous transluminal coronary angioplasty (PTCA) in 1981 extended the theoretic pressure range available for dilatation from 7 atm to 13 atm. The impact of higher dilatation pressure on results of PTCA was studied. The last 100 consecutive patients treated exclusively with the old balloon type (low-pressure group) were compared to the first 100 consecutive patients treated exclusively with the new balloon type (high-pressure group). There was no difference in age, sex, artery distribution, initial degree of stenosis, and initial pressure gradient between the two groups. The mean peak pressure applied was 7.0 +/- 1.6 atm in the low-pressure group and 8.5 +/- 2.1 atm in the high-pressure group (p less than 0.001). The average balloon diameter used and the number and duration of balloon fillings were similar in both groups. Primary success, complications, and residual degree of stenosis were not different in the two groups. The residual pressure gradient, however, was significantly lower in the high-pressure group (11 +/- 7 mm Hg) than in the low-pressure group (16 +/- 10 mm Hg) (p less than 0.01). This indicates a better immediate hemodynamic result without increased risk. It is concluded that it is safe to perform PTCA with the new balloon types allowing for higher pressures. The increment in average pressure used for dilatation, which occurred incidentally, improved the average hemodynamic outcome. This may influence recurrence rate and deserves further investigation by randomized trials.