Once inside a blocked artery, it is able to release drugs to dissolve blood clots, which are often the cause of heart attacks.
The robot has three short front legs and three longer back legs which are attached to a central rectangular body.
By attaching grafted heart muscle to the legs, the scientists found the legs would bend as the muscle cells contracted. The cells get their energy from sugar in the patient's blood.
That means the robot does not need an external power supply, which are often heavy and cumbersome, if not impractical.
Because the robot's three front legs are shorter than the back legs, they bend inwards as the heart muscles contract, creating a difference in friction that pushes the robot forward.
Using cells from the patient's own body – perhaps grown from stem cells – would also reduce the likelihood of the body producing an immune reaction, which might destroy the tiny robot before it could clear a blockage.