A tissue puncture assembly includes an elongate tubular member having a lumen, a distal portion having a side wall, a side port opening extending through the side wall and, and a guiding surface having a distal end that extends adjacent to a distal edge of the side port opening. The tissue puncture assembly further includes a flexible puncture member insertable through the lumen of the elongate tubular member. The flexible puncture member deflects upon contacting the guiding surface to exit the elongate tubular member through the side port in a lateral direction relative to a longitudinal direction of the elongate tubular member. The tissue puncture member is capable of puncturing tissue at an oblique angle. The tissue puncture member may further adopt a pre-formed shape at its distal end to prevent inadvertent puncture of tissue and to maintain access to the puncture site. The transseptal puncture assembly may include various sensors to identify tissue structures and precisely locate the desired puncture site.
