Apparatus and methods are described, including a blood pump that includes a catheter, a proximal impeller disposed on the catheter inside a proximal impeller housing, and which is configured to pump blood by rotating inside the proximal impeller housing. A distal impeller is disposed on the catheter inside a distal impeller housing, distally to the proximal impeller, and the distal impeller is configured to pump blood by rotating inside the distal impeller housing. A tubular element is disposed between the proximal impeller housing and the distal impeller housing, the tubular element being configured to have a tubular configuration during rotation of the proximal and distal impellers. Other applications are also described.