Abstract: Methods, systems, devices and computer program products for providing maintenance, guidance and/or control of certain systems are disclosed. Typically, in some aspects the systems are complex. Also disclosed are methods, systems, devices and computer program products for providing therapeutic guidance for controlling a subject's circulation. One such method comprises the steps of: (i) determining the subject's present and desired circulatory states as a function of at least mean systemic filling pressure (Pms), heart efficiency (EH) and systemic vascular resistance (SVR); (ii) determining a target direction of a trajectory from the subject's present circulatory state to said subject's desired circulatory state, wherein treatment of the subject so as to traverse the trajectory will cause the subject's circulatory state to move towards a desired circulatory state; and (iii) visually representing the target direction of the trajectory.