A 66-year-old female with a medical history of type 2 diabetes mellitus, hypercholesterolaemia, mild renal impairment, and cardiac catheterization in 2012 for symptoms of angina (no significant coronary artery disease) presented to the emergency department with symptoms of fatigue and diarrhoea for the last 10 days. She reported coughing in the last few days and had visited a sister-in-law positive for COVID-19. She used gliclazide 60 mg once daily, lisinopril 10 mg once daily, and metformin 200 mg twice daily, and had been prescribed ciprofloxacin 500 mg twice daily the day before by her general practitioner to treat her symptoms. On arrival to the emergency department, body temperature was 38°C, blood pressure 98/69 mmHg, with a heart rate of 92 b.p.m. Her oxygen saturation was 94% with 12 L of O2 per minute through a non-rebreather mask. Pulmonary examination revealed tachypnoea and bilateral coarse crackles upon auscultation. Her heart rhythm was regular with normal first and second heart sounds without murmurs. Findings on chest radiography showed a multifocal, bilateral, and peripheral ground-glass pattern. Blood tests demonstrated increased C-reactive protein levels of 113 mg/L (reference value <10 mg/L), impaired renal function with creatinine levels of 107 μmol/L (reference value 50–90 μmol/L) and CKD-EPI of 47 mL/min/1.73 m2 (reference value >90 mL/min/1.73 m2), with normal levels of potassium and sodium. The patient was admitted to the internal medicine ward. Ceftriaxone 2 g once daily was administered intravenously, while ciprofloxaxin was discontinued. COVID-19 was confirmed by a nasopharyngeal swab testing positive for SARS-CoV-2 using real-time reverse transcription–polymerase chain reaction (RT–PCR) assay. Several hours after the patient’s admission, her clinical condition worsened. Antiviral therapy with chloroquine was initiated according to recent guidelines, with a loading dose of 600 mg orally and a maintenance dose of 300 mg twice a day for a total of 5–7 days. The 12-lead ECG at baseline showed a QTc interval of 429 ms. In the days thereafter, her condition progressively deteriorated, with oxygen saturation <90% and increased respiratory effort. She was then transferred to the ICU for mechanical ventilation on the third day of admission. Chest CT on the fifth day of admission showed widespread bilateral ground-glass opacities and consolidations in the lower lobes, but also bilateral segmental and subsegmental pulmonary embolisms. Because of QTc prolongation (QTc interval 482 ms), treatment with chloroquine was discontinued on the fifth day of admission. Unfortunately, treatment with erythromycin 250 mg twice daily started on the sixth day of admission to improve gastrointestinal motility. At the start of erythromycin treatment the QTc interval was 453 ms. On the seventh day of admission, the patient was resuscitated because of TdP (). Erythromycin was discontinued and concomitant treatment with 2 g of intravenous magnesium was initiated. Retrospective evaluation of the multiple-lead telemetric monitor showed progressive QTc interval prolongation with a duration up to 550 ms and development of large U waves (). Bradycardia and late coupled ventricular ectopy in bigeminy resulted in short–long–short interval-initiated TdP (). Reversible causes of QT interval prolongation were investigated. Blood tests showed restored renal function and normal levels of electrolytes, with the exception of phosphate (0.88 mmol/L; reference value 0.90–1.50 mmol/L), which was corrected with oral glycophosphate. Acute ischaemia was excluded, with no significant rise or fall in high sensitivity troponin T. Transthoracic echocardiogram showed normal dimensions of the ventricles with normal systolic function (left ventricular ejection fraction ±50%). The patient’s past medical history made significant coronary artery disease as a contributing factor unlikely. Earlier ECG registrations and treadmill testing from 2012 up to 2017 showed a normal QT interval, making underlying congenital long QT unlikely. Continued close monitoring of the QT interval showed no recurrent episodes of TdP. On the eighth day of admission, the QTc interval was 507 ms () and, on the 16th day of admission, the QTc interval was almost completely normal (). The patient recovered gradually and was tested negative for COVID-19 on the 52nd day of admission. She was discharged from the hospital on the 62nd day of admission to a rehabilitation centre. After full recovery, appropriate long QT analysis will be conducted.