The Monday Effect: Weekly and Circadian Patterns in Acute Cardiovascular Emergencies Monday Effect in Cardiovascular Emergencies

<i>Background and Objectives:</i> Monday syndrome refers to a psychosomatic stress response occurring at the beginning of the work week and has been implicated in triggering acute cardiovascular events. This study aimed to evaluate the association between Monday syndrome and the incidence of cardiovascular emergencies. <i>Materials and Methods:</i> Between June 2024 and June 2025, a total of 500 patients aged 18-65 years who presented with acute cardiovascular events at two centers were retrospectively analyzed. Diagnoses included STEMI, NSTEMI, unstable angina, ventricular tachycardia/fibrillation, and hypertensive emergency. The distribution of events by weekday and hour was examined. Poisson regression was used to assess the effect of Mondays on event incidence. <i>Results:</i> Of 500 patients (mean age 49.1 ± 9.7 years, 50.4% male), the most common diagnoses were STEMI (31.8%) and NSTEMI (27.4%). The incidence of cardiovascular events was highest on Mondays (19.6%) and lowest on Sundays (10.6%). The early-morning period (06:00-10:00) showed the most significant clustering of events (<i>p</i> < 0.001). Systolic blood pressure (145 ± 18 vs. 139 ± 17 mmHg, <i>p</i> = 0.008) and heart rate (87 ± 12 vs. 82 ± 13 bpm, <i>p</i> = 0.01) were significantly higher on Mondays. Monday presentation was associated with a 23% higher event rate (incidence rate ratio [IRR] 1.23, 95% CI 1.10-1.38, <i>p</i> = 0.002). <i>Conclusions:</i> Monday syndrome is associated with a significant increase in the incidence of cardiovascular emergencies, especially in the early-morning hours. Increased sympathetic tone, hormonal activation, and psychosocial stress are possible contributors.