svtsim is a web-based cardiac electrophysiology study (EPS)/arrhythmia simulator, which is primarily designed for training and education. Its target audience includes cardiology and clinical cardiac electrophysiology fellows-in-training and electrophysiology laboratory nurses and technicians. svtsim provides an environment to simulate different cardiac arrhythmias and it allows the user to perform various diagnostic maneuvers by pacing the simulated heart in realtime.