We have been developing a wearable pneumatic total artificial heart (PTAH) system for bridge to transplant, and we evaluated its fundamental performance in in vitro and in vivo experiments. The PTAH system consists of left and right diaphragm-type blood pumps and a compact wearable pneumatic drive (WPD-100) unit. The WPD-100 unit can generate a fixed systole ratio by the non-circular gears. The prototype WPD-100 units with fixed systolic ratio of 35, 40 and 44% were developed. 25 mm and 23 mm Bicarbon valves were mounted in the inlet and outlet ports of the left and right blood pumps. As a result of an overflow-type mock circulation test, more than 8.0 l/min of pump output was obtained at 100 bpm for after load of 80, 100 and 120 mm Hg in all WPD-100 units. An acute animal experiment was also performed using WPD-100 units with fixed systolic ratio of 35 and 44% in a calf weighing 98 kg. The cardiac output ranged between 4.3 and 5.2 l/min at the mean aortic pressures of 108-115 mm Hg at beating rates of 60 to 100 bpm. These results indicated that our PTAH system consisting of two blood pumps and WPD-100 units have sufficient performance for total cardiac replacement.