An implantable vascular access port system, comprising: a vascular access port configured for implantation within a body of a patient; and a catheter operably connected to the access port and configured for insertion into a vasculature of the patient, the catheter including: an elongate catheter tube defining a proximal portion and a distal portion, the catheter tube defining at least one lumen that extends from a proximal end to a distal end of the catheter tube, the proximal portion defining a first cross sectional lumen area, the distal portion defining a second cross sectional lumen area larger than the first cross sectional lumen area so as to prevent whipping of the distal portion of the catheter when the catheter is disposed within the vasculature of the patient and a fluid is passed through the at least one lumen, a taper region interposed between the proximal and distal portions, the taper region transitioning in size from the first cross sectional lumen area to the second cross sectional lumen area, wherein the proximal portion of the catheter tube further includes a proximal taper region adjacent the proximal end of the catheter tube, the proximal taper region transitioning in size from a third cross sectional lumen area at the proximal end of the catheter tube to the first cross sectional lumen area of a more distal segment of the proximal portion of the catheter tube, the third cross sectional lumen area greater relative the first cross sectional lumen area, wherein the proximal end of the catheter tube is operably connected to a stem of the access port, the stem being sized to operably connect within the third cross sectional lumen of the proximal taper region of the catheter tube in a fluid-tight configuration, the inner diameter of the stem matching the cross-sectional area of the lumen in the proximal taper region. a vascular access port configured for implantation within a body of a patient; and a catheter operably connected to the access port and configured for insertion into a vasculature of the patient, the catheter including: an elongate catheter tube defining a proximal portion and a distal portion, the catheter tube defining at least one lumen that extends from a proximal end to a distal end of the catheter tube, the proximal portion defining a first cross sectional lumen area, the distal portion defining a second cross sectional lumen area larger than the first cross sectional lumen area so as to prevent whipping of the distal portion of the catheter when the catheter is disposed within the vasculature of the patient and a fluid is passed through the at least one lumen, a taper region interposed between the proximal and distal portions, the taper region transitioning in size from the first cross sectional lumen area to the second cross sectional lumen area, wherein the proximal portion of the catheter tube further includes a proximal taper region adjacent the proximal end of the catheter tube, the proximal taper region transitioning in size from a third cross sectional lumen area at the proximal end of the catheter tube to the first cross sectional lumen area of a more distal segment of the proximal portion of the catheter tube, the third cross sectional lumen area greater relative the first cross sectional lumen area, wherein the proximal end of the catheter tube is operably connected to a stem of the access port, the stem being sized to operably connect within the third cross sectional lumen of the proximal taper region of the catheter tube in a fluid-tight configuration, the inner diameter of the stem matching the cross-sectional area of the lumen in the proximal taper region.