Holiday heart syndrome (HHS) is the medical name for sudden cardiac arrhythmias — most commonly atrial fibrillation — triggered by binge drinking in people with otherwise healthy hearts. First described by cardiologist Dr. Philip Ettinger in 1978 after observing a Monday-morning spike in arrhythmia hospitalizations following weekend drinking, HHS has since been replicated in dozens of studies. The landmark 2017 Munich Beer-Related Electrocardiogram Workup (MunichBREW) followed 3,028 Oktoberfest attendees and found roughly 30% had measurable arrhythmias — most resolved within hours of becoming sober. Three mechanisms combine to push the atria into unstable rhythm during and after a binge. First, alcohol withdrawal triggers a sympathetic surge — adrenaline and noradrenaline release shortens atrial refractory period and creates conditions for AFib. Second, alcohol's diuretic effect depletes potassium and magnesium, both essential for stable cardiac conduction. Third, acetaldehyde — alcohol's primary metabolite — is directly toxic to atrial cells, causing transient inflammation. Risk scales with both amount and speed: occasional drinking up to 1 drink/day shows roughly baseline risk, but 5+ drinks in a single session raises same-day AFib risk by 38% (Marcus 2021). Habitual heavy drinking 2–3× lifetime AFib risk. HHS typically presents 12–36 hours after binge — often Sunday morning after Saturday night. Symptoms include fluttering or pounding sensation in the chest, irregular pulse, shortness of breath, lightheadedness, anxiety, and disproportionate fatigue. About 90% of cases convert back to normal sinus rhythm spontaneously within 24 hours of BAC reaching zero. The remaining 10% may need medical cardioversion. Seek emergency care for chest pain, severe shortness of breath, fainting, resting pulse over 150 bpm, or symptoms lasting beyond 6 hours. Even self-resolving episodes warrant a follow-up — a first AFib episode triples lifetime recurrence risk. Prevention is straightforward: cap intake at 1 drink/hour, alternate with water, eat before drinking, avoid energy-drink mixers. Sources: Ettinger 1978, MunichBREW (Brunner 2017), Csengeri 2021 EHJ, Marcus 2021 Annals of Internal Medicine, Tonelo 2013.