At Day 0 (2022), a 73-year-old male with known ATTRwt presented to the outpatient clinic with shortness of breath, mild swelling of the lower legs, and palpitations with onset within the recent 2 weeks. Three years prior, he was diagnosed with ATTRwt following participation in a screening trial for transthyretin amyloidosis (ATTR) in patients with previous carpal tunnel surgery. At diagnosis, he was asymptomatic without any history of cardiovascular disease. His electrocardiogram (ECG) showed sinus rhythm with borderline low voltage in the limb leads, and N-terminal prohormone of brain natriuretic peptide (NT-proBNP) was slightly elevated at 390 ng/L (normal < 300 ng/L). Echocardiography demonstrated mild increased left ventricular (LV) wall thickness of 12 mm, LV ejection fraction (LVEF) 70%, and normal LV global longitudinal strain (LVGLS) −18.8% with borderline apical sparring pattern ( and ). The diagnosis of ATTRwt was established by a positive bone scintigraphy—Perugini grade 2 (see )—and by endomyocardial biopsy. Genetic testing was negative for variant ATTR. He was subsequently followed untreated for 3 years with stable parameters. At Day 0, cardiac examination of the patient showed mild leg oedema, no heart murmurs, irregular heart rate of 110 b.p.m., elevated blood pressure (150/80 mmHg), ECG with atrial fibrillation, and frequent ventricular ectopy (). Echocardiography revealed LVEF 57%, increased wall thickness of 14 mm, and tricuspid regurgitant gradient of 18 mmHg. Serum NT-proBNP was 436 ng/L. No further imaging was ordered. Furosemide (40 mg daily), low dosage of metoprolol (50 mg daily), and dabigatran (150 mg × 2 daily) were initiated immediately. Following discharge, a 48-h Holter monitoring was performed and a direct current cardioversion (DCC) preceded by transoesophageal echocardiography was planned within 3–4 weeks. However, at Day 7, the Holter monitoring analysis revealed that the atrial fibrillation ceased after 2 h and sinus rhythm remained subsequently. Unexpectedly, three episodes of symptomatic (palpitations) monomorphic ventricular tachycardia (VT) was observed with a frequency of 255 b.p.m. and a duration of 40–60 s (). In addition, ∼20% of total beats were ectopic unifocal ventricular beats. At Day 8, the coronary angiography demonstrated a highly significant stenosis of the proximal left anterior descending artery (LAD) which was treated by direct percutaneous coronary intervention (PCI) (see and ). Clopidogrel 75 mg × 1 was added with a treatment duration of 12 months. The unifocal ventricular ectopy vanished immediately after the PCI as observed by in-hospital cardiac telemetry, and the patient was asymptomatic at same-day discharge. At Days 12–14, as a consequence of the characteristics of the monomorphic VT, the ATTRwt diagnosis, and the presence of paroxysmal atrial fibrillation, it was decided by consensus to implant a dual chamber implantable cardioverter defibrillator (DDD-ICD). Tafamidis was not considered as it is not currently approved by Danish Health Authorities. At 1- and 3-month follow-up (Day 42/110), the patient was well-being and asymptomatic. The ECG (), a 48-h Holter monitor examination and ICD interrogation revealed persistence of sinus rhythm, no recurrent VT, and a marked reduction of ventricular ectopic beats to <1% of total beats. Echocardiography demonstrated minor subclinical changes with a reduction of LVEF to 60% and LVGLS to −15.6% with local mildly reduced LV strain values in the anterolateral segments () (see ). N-terminal prohormone of brain natriuretic peptide was 537 ng/L.