Abstract: A cardiac stimulation system and method delivers a left ventricle stimulator from a right ventricle lead system in the right ventricle chamber, into a right side of an interventricular septum at a first location, and transmuscularly from the first location to a second location along the left side of the septum. The left ventricle stimulator is affixed at the second location for transmuscular stimulation of the left ventricle conduction system. A biventricular stimulation system further includes a right ventricle stimulator also delivered by the right ventricle lead system to the first location along the right side of the septum for right ventricular stimulation. An energy source is coupled to the transmuscular stimulation system, i.e., a pacemaker, and/or defibrillator, or to enhance contractility, and may be coupled directly or via “leadless” system(s). Various highly beneficial particular arrangements of stimulators and leads are further described.