  We investigate the rectification of thermal fluctuations in a mesoscopic
on-chip heat engine. The engine consists of a hot chaotic cavity capacitively
coupled to a cold cavity which rectifies the excess noise and generates a
directed current. The fluctuation-induced directed current depends on the
energy asymmetry of the transmissions of the contacts of the cold cavity to the
leads and is proportional to the temperature difference. We discuss the maximal
power output of the heat engine and its efficiency.
