Navigator methods are disclosed that are based on detecting a flow-sensitive signal within a subject, and using the position of the signal to track subject motion between imaging sequences. In a disclosed embodiment, the fast-moving blood volume in the left ventricle of the heart is detected and used as a reference point to correct for cardiac motion that results from respiratory motion in a subject. The navigator based on the position of the fast-moving blood volume in the left ventricle may be applied prospectively to shift a subsequent imaging slice to compensate for subject motion, and thereby provide MRI images with increased clarity and resolution.