A previously healthy 44-year-old man was admitted to our hospital for severe dyspnea and syncope on March 25 th , 2020. Seven days before, during the escalating Covid-19 pandemic in our country, he presented at the Emergency Department with fever, dry cough, diarrhea and myalgia, being diagnosed as presumed Covid-19 infection. He was discharged home with symptomatic therapy and isolation measures. However, symptoms worsened over the following days and finally he came back with severe bradycardia, hypotension and signs of peripheral hypoperfusion. The ECG showed a third-degree atrioventricular block ( Figure   1A ) and echocardiography revealed a non-dilated but globally and severely dysfunctional left ventricle (left ventricular ejection fraction [LVEF] ~15%) (Video 1). A temporary pacemaker was implanted and both dobutamine and norepinephrine perfusions were initiated but, eventually, intubation and mechanical ventilation was required. High-sensitive troponin T peak was 745 ng/L, creatine-kinase isoenzyme MB 30 U/L, and NT-proBNP raised to 24,167 pg/mL. Nasopharyngeal and oropharyngeal swabs for PCR test of Covid-19 and other respiratory viral infections were obtained. Only Sars-CoV-2 resulted positive, while influenza A virus, influenza A H1N1, influenza A H3N2, bocavirus, adenovirus, rhinovirus, parainfluenza, metapneumovirus, influenza B virus, other common coronavirus, and respiratory syncytial virus were negative. Legionella pneumophilla, Mycoplasma pneumoniae and Chlamydophila pneumonia serological tests resulted negative. Chest X-ray showed signs of bilateral pneumonia ( Figure 1B) . In spite of increasing doses of vasoactive drugs, hemodynamic derangement ensued and in this dramatic clinical scenario urgent coronary angiography revealed normal coronary arteries. Venous-arterial extracorporeal membrane oxygenation (VA-ECMO), ( Figure 1C ) and an intra-aortic balloon pump were implanted through femoral cannulation with drastic improvement of the hemodynamic condition.
Several endomyocardial biopsy (EMB) samples were obtained ( Figure 1D) . A working diagnosis of "fulminant myocarditis" was made, and a 1,000 mg bolus of methylprednisolone was administered followed by treatment with tocilizumab hydroxychloroquine, azithromycin and lopinavir-ritonavir. Blood tests showed abnormal values of D-dimer (3.17 µg/mL), ferritin (1,135 ng/ml) and circulating interleukin-6 (121.71 pg/L). Myocardial samples showed no significant inflammatory infiltrates, even after CD3, CD20 and CD68 staining ( Figure 1E -F) and steroid therapy was withheld. Clinical status improved during the following days, with a rapid reduction of lactate levels to normal values, normalization of kidney and liver functions, and progressive recovery in left ventricular systolic function (Video 2). Blood tests showed reduction of high-sensitive troponin T levels to 221 ng/L and NT-proBNP to 7624 pg/ml. VA-ECMO and the intra-aortic balloon could be successfully withdrawn six days after implant and the patient could be eventually weaned from ventilation 2 days later. On day 14 from admission a cardiac magnetic resonance was performed. A nondilated left ventricle without regional wall motion abnormalities was seen (LVEF ~75%) (Video 3). Native T1 (mean 1120ms), T2 signal intensity ratio (myocardium to serratus anterior muscle on T2 images processed by a signal intensity correction algorithm) and extracellular volume (mean 36%), were diffusely increased with a slightly less involvement of inferolateral wall ( Figure 1G-I) . Late gadolinium enhancement was negative The year 2020 will be remembered for the world pandemic due to coronavirus (2019-nCoV) infection. Covid-19 morbidity and mortality are mainly associated with lung involvement. However, underlying cardiovascular conditions play a major role on clinical outcomes(1). Moreover, recent studies suggest that cardiac injury has important prognostic implications. Elevations in cardiac troponins are frequently seen with clinically evident myocardial damage demonstrated in most severe cases(1). However, so far, only a few cases of Covid-19-related myocarditis have been described (3) (4) (5) . Unspecific pathological findings have been described in isolated reports with only one necropsy study reporting mild inflammatory infiltrate (5) . However, we report the successful treatment of cardiogenic shock with temporary mechanical circulatory support in a patient with a clear diagnosis of infection presenting as fulminant myocarditis. Takotsubo cardiomyopathy remains a potential differential diagnosis considering the stressful situation, the myocardial edema and transient left ventricular dysfunction. A wide phenotypic presentation of myocardial damage appears to exist in Covid-19 patients, ranging from mild myocardial injury (asymptomatic troponin elevation) to severe forms of myocarditis (likely secondary to the cytokine storm). The absence of scar might be a clinical marker of myocardial recovery. The fact that cardiac function fully recovered after a few days of mechanical circulatory support is of major interest, opening new avenues for the management of critically-ill Covid-19 patients with fulminant myocarditis, as complete recovery of the myocardial function can be expected.
The patient provided informed consent to publish his data but institutional review board approval was not requested considering that this was a clinical observation obtained in a single patient that was strictly treated according to standard clinical practice. EMB without necrosis, inflammation or fibrosis (HEx200). F) Isolated intersticial infiltrate with lymphocytes CD3+ (yellow arrows). G-H) T2 weighted and T2 signal intensity ratio mapping images (blue indicates a ratio more than 2) showing diffuse edema with slightly less involvement of inferolateral wall. I) T1 mapping with diffuse increase of native T1 (septal T1= 1120ms) following the pattern of edema.
Supplementary figure. Late gadolinium enhancement without macroscopic necrosis.
Video 1: Pre-ECMO echocardiographic subxiphoid view.Video shows a non-dilated but globally and severely dysfunctional left ventricle.
Post-ECMO echocardiographic subxiphoid view. Video illustrates complete recovery in left ventricular systolic function.
Post-ECMO cardiac magnetic resonance 4-chamber view cine. Video shows a nondilated left ventricle with normal systolic function.