The RCVSIM source code was written predominantly in the MATLAB language (version 5.3.1; R11.1) and includes some C language necessary for on-line viewing and parameter updating. The source code may be compiled using the MATLAB compiler (version 1.2) with the libc5 development environment at the MATLAB prompt (see Section 4.2). Note that compilation permits software execution at the Linux prompt and greatly improves execution speed. The source code not only consists of code to implement the models described in Section 2 but also includes code to implement other models. These latter models have been minimally tested and documented and may only be executed in the MATLAB environment. A description of the code for implementing the models of Section 2 and an explanation of how this code may be modified or extended to implement arbitrary lumped parameter cardiovascular models are provided below. See Appendix A for a brief description of the other models and the source code for executing them.