A balloon dilation catheter includes a dilation balloon and a shaft having a coaxial portion including an outer tubular member having a bore, a proximate end and a distal end and a transition neck formed at the distal end of the coaxial portion, the transition neck having a proximate end at the distal end of the outer tubular member and a distal end, an access fitting adjacent the proximate end of the catheter shaft for directing a guidewire into the catheter shaft, an inflation port for directing an incompressible inflation medium into the catheter shaft, a guidewire tubular member disposed coaxially in the outer tubular member and extending continuously through the outer tubular member to the distal end of the outer tubular member and through the transition neck, the outer tubular member and guidewire tubular member defining a first, annular inflation/deflation lumen therebetween in fluid communication with the inflation port, at least one second inflation/deflation lumen formed through the transition neck, the second inflation/deflation lumen separate from and non-coaxial with the guidewire tubular member and having a cross-sectional area less than the cross-sectional area of the first inflation/deflation lumen and opening at a proximate end into the first inflation/deflation lumen and at the distal end of the transition neck whereby the second inflation/deflation lumen provides fluid communication from the first inflation/deflation lumen through the transition neck such that inflation fluid passing through the first inflation lumen may flow though the second inflation/deflation lumen and directly into the dilation balloon.