Heart transplant recipients (n = 11) were studied before discharge from the hospital and 1, 3, 6, and 12 months after transplantation to (1) examine systolic and diastolic blood pressure and heart rate circadian patterns, (2) detect the presence or absence of nocturnal declines, and (3) describe changes in the mean levels of systolic blood pressure, diastolic blood pressure, and heart rate. An ambulatory blood pressure-monitoring system was used to record blood pressure and heart rate at 1-hour intervals for up to 48 hours. Data were analyzed with descriptive and independent t-test statistics, as well as cosinor analysis for rhythmicity. The majority of the patients had significant (p < 0.05) circadian rhythms for systolic and diastolic blood pressure and heart rate throughout the study, but at times the systolic and diastolic blood pressure acrophases were found to be phase shifted to earlier or later along the time axis (e.g., peak values occurring at 3 AM rather than later in the morning or early afternoon), such that no relationships were found between circadian rhythms and nocturnal declines. More "normal" circadian rhythms were observed for heart rate than for systolic and diastolic blood pressures. The development of hypertension (systolic/diastolic blood pressures > 140/90 mm Hg) was common and by 6 months and 1 year after transplantation 8 of the 10 patients remaining in the study were hypertensive. Increases in mean heart rate of approximately 18% (ranging from 2% to 46%) were also observed during the first postoperative year.