A 27 year old woman who had undergone closed heart surgical commissurotomy 10 years previously, underwent percutaneous mitral valvuloplasty during the fourth month of her pregnancy. Despite significant valvular thickening with calcification, the balloon dilatation led to an increase in valve surface area from 1.1 to 2 cm2 with no complications and with relief of the pulmonary hypertension. Foetal protection against ionising radiation was assured by a lead mantle completely surrounding the patient's abdomen. This protection reduced irradiation of the pelvic region to 0.5 milliSievert which corresponds to 1/100 of the permitted irradiation of pregnant women professionally exposed to ionising radiation.