In coronary angioplasty (PTCA) stenoses over 80% can usually be passed with very small catheters only. To pass stenoses with different catheters during one procedure may be dangerous because of dissection. We therefore developed an instrument with very small tip-diameter and two balloons of different diameters in series. In 9 cases primary success was achieved and the degree of stenoses reduced from 90% to 23%. The gradient was 58 mmHg and remained only 11 mmHg after PTCA. When used with caution, the advantage of this catheter in high degree coronary stenoses is obvious.