Effective dose is an important quantity in relation to assessment of radiation risk. Organ and effective doses to paediatric patients undergoing diagnostic and therapeutic heart catheterization procedures can be assessed by combining relatively simple measurements, e.g. of dose-area product (DAP), and calculated dose conversion factors (DCF). This also holds for the radiation dose to the hospital staff, e.g. the cardiologist. Monte Carlo (MC) simulation of radiation transport in mathematical anthropomorphic phantoms is used to obtain the DCFs, which strongly depend on beam quality and geometrical parameters. The performance of a dedicated fast MC code (PCXMC) for patient dosimetry is compared with that of a more elaborate general purpose MC code (MCNP). Resulting organ doses sometimes may differ considerably, partly due to phantom differences. While MCNP uses separate male and female mathematical phantoms, PCXMC uses a hermaphrodite. However, both codes yield effective doses that agree rather well, so PCXMC can be used for convenience. The MCNP code is used to calculate the effective dose to the cardiologist exposed to radiation scattered from the patient. Without protective clothing, effective dose per procedure to the cardiologist is at least two orders of magnitude lower than that to the patient. The effectiveness of various types and thickness of protective clothing has been evaluated for one view of one cardiac catheterization. The results of the calculations do not contradict experimental studies from the literature. MC simulation may serve as a useful tool to improve the accuracy of estimating occupational effective dose from personal dose monitors.