Apparatus and methods are described including a catheter, and first and second impellers configured to be inserted into a subject's body via the catheter, the first and second impellers being disposed in series with each other. A motor is configured to generate rotational motion. A rotation shaft extends from the motor to the first impeller and imparts the rotational motion from the motor to the first impeller. A gear mechanism disposed between the first and second impeller is configured to effect a change in rotational motion that is imparted from the first impeller to the second impeller, such that the second impeller rotates in a different manner from the first impeller. Other applications are also described.