A multiple catheter assembly, comprising: a first catheter comprising a first proximal end region, a first lumen extending through the first catheter, and a first distal end region terminating in a first distal tip, at least a portion of the first catheter residing in a cannulating portion, the first catheter further comprising a first catheter wall defining at least the first lumen and further defining a cross-section at the first distal tip and a cross-section in the cannulating portion, the first lumen defining a cross-section at the first distal tip and a cross-section in the cannulating portion, and a second catheter comprising a second proximal end region, a second lumen extending through the second catheter, and a second distal end region terminating in a second distal tip, at least a portion of the second catheter residing in the cannulating portion, the second catheter further comprising a second catheter wall defining at least the second lumen and further defining a cross-section at the second distal tip and a cross-section in the cannulating portion, the second lumen defining a cross-section at the second distal tip and a cross-section in the cannulating portion, characterized in that the first distal end region comprises a first transition region transitioning the first catheter wall from the cross-section defined by the first catheter wall at the first distal tip to the cross-section defined by the first catheter wall in the cannulating portion, the first transition region further transitioning the first lumen from the cross-section defined by the first lumen at the first distal tip to the cross-section defined by the first lumen in the cannulating portion, and the second distal end region comprises a second transition region transitioning the second catheter wall from the cross-section defined by the second catheter wall at the second distal tip to the cross-section defined by the second catheter wall in the cannulating portion, the second transition region further transitioning the second lumen from the cross-section defined by the second lumen at the second distal tip to the cross-section defined by the second lumen in the cannulating portion, wherein the cross-section defined by the first lumen at the first distal tip is different from the cross-section defined by the second lumen at the second distal tip, and wherein the first and second lumens (311, 341) are independent from each other for facilitating simultaneous flow in opposite directions. a first catheter comprising a first proximal end region, a first lumen extending through the first catheter, and a first distal end region terminating in a first distal tip, at least a portion of the first catheter residing in a cannulating portion, the first catheter further comprising a first catheter wall defining at least the first lumen and further defining a cross-section at the first distal tip and a cross-section in the cannulating portion, the first lumen defining a cross-section at the first distal tip and a cross-section in the cannulating portion, and a second catheter comprising a second proximal end region, a second lumen extending through the second catheter, and a second distal end region terminating in a second distal tip, at least a portion of the second catheter residing in the cannulating portion, the second catheter further comprising a second catheter wall defining at least the second lumen and further defining a cross-section at the second distal tip and a cross-section in the cannulating portion, the second lumen defining a cross-section at the second distal tip and a cross-section in the cannulating portion, characterized in that the first distal end region comprises a first transition region transitioning the first catheter wall from the cross-section defined by the first catheter wall at the first distal tip to the cross-section defined by the first catheter wall in the cannulating portion, the first transition region further transitioning the first lumen from the cross-section defined by the first lumen at the first distal tip to the cross-section defined by the first lumen in the cannulating portion, and the second distal end region comprises a second transition region transitioning the second catheter wall from the cross-section defined by the second catheter wall at the second distal tip to the cross-section defined by the second catheter wall in the cannulating portion, the second transition region further transitioning the second lumen from the cross-section defined by the second lumen at the second distal tip to the cross-section defined by the second lumen in the cannulating portion, wherein the cross-section defined by the first lumen at the first distal tip is different from the cross-section defined by the second lumen at the second distal tip, and wherein the first and second lumens (311, 341) are independent from each other for facilitating simultaneous flow in opposite directions.