A ventricular assist system and a blood pump controller including a blood pump usable in a state where a first slide surface and a second slide surface are brought into contact with each other, and a cool sealing liquid is supplied to a gap formed between the first slide surface and the second slide surface; a first sub controller having a first cool sealing liquid reservoir, a cool sealing liquid pump, a first pipe joint upstream side, and a fourth pipe joint downstream side; and a second sub controller having a blood pump drive circuit, a battery, a first pipe joint downstream side, a second pipe joint upstream side, a third pipe joint downstream side, and a fourth pipe joint upstream side. The first sub controller and the second sub controller are detachably connected by a first pipe joint and a fourth pipe joint.