Systems and methods for transeptal cardiac procedures are disclosed. A patient treatment device in accordance with a particular embodiment includes an elongated intravascular guidewire that includes a first branch and a second branch fixedly secured relative to the first branch at a first location and releasably secured relative to the first branch at a second location. At least one of the first and second branches is movable relative to the other between a first position in which the first and second branches form a closed shape, and a second position in which the first and second branches form an open shape. A controller can be operatively coupled to the first and second branches to control (e.g., in a fixed increment manner or a continuously variable manner) a distance between a portion of the first branch and a portion of the second branch while the first and second branches form the closed shape.