In a prospective study the authors investigated 30 pregnant women (mean age 27 +/- 5.5 years) with prolapse of the mitral valve confirmed on echocardiography, without significant mitral regurgitation, in order to assess whether mitral valve prolapse is a risk factor for the development of complications during gestation and childbirth. As control served a group of 30 healthy pregnant women of corresponding age and number of previous pregnancies, incidence of complications during pregnancy, the type of delivery, sex, length, weight and maturity of the neonates. In women with mitral valve prolapse the authors recorded a significantly higher incidence of subjective complaints such as palpitations associated in 7 of 8 cases with sinus tachycardia 110-140/min. at rest and with vasovagal syncopes. The palpitations were always favourably influenced by beta-blocker therapy or by calcium antagonists. Mitral valve prolapse without haemodynamically significant mitral regurgitation during pregnancy is not a significant risk factor for the development of complications.