It is well known that both normal subjects and hypertensives manifest a distinct nocturnal fall of arterial blood pressure and heart rate. But till now there has been no report about the diurnal change of blood pressure and heart rate in MVP patients. In this report we studied the circadian variations of blood pressure and heart rate in 18 symptomatic MVP patients (mean age 32 +/- 10 years) and compared them with those in 18 age- and sex-matched normal control subjects (mean age 35 +/- 9 years). The MVP group presented a statistically significant blunting of the nocturnal fall in systolic blood pressure (4.2 +/- 3.6% vs 9.7 +/- 3.7%, p = 0.0002). No obvious difference in the nocturnal fall in heart rate was noted between both groups (20.2 +/- 6.0% vs 18.8 +/- 5.6%, p = 0.4290). In conclusion, the circadian variation of blood pressure was blunted in patients with mitral valve prolapse. The mechanism is uncertain and further studies are necessary to clarify it.