A 68-year-old woman was admitted to the intensive care unit with respiratory failure and hypotension. Her blood pressure was 70/50 mm Hg, and her heart rate was 125 beats per minute. Physical examination revealed skin mottling on the legs (Panel A). Laboratory values were notable for an arterial-blood lactate level of 4.5 mmol per liter (normal value, <2.0), a cardiac troponin T level of 0.43 ng per milliliter (normal value, <0.014), an N-terminal pro–brain natriuretic peptide level of 24,500 pg per milliliter (normal value, <900), and a positive polymerase-chain-reaction assay for adenovirus in bronchoalveolar-lavage fluid and blood. No other viruses or bacteria were found. Transthoracic echocardiography revealed a left ventricular ejection fraction of 25%. Skin mottling, a common clinical sign in patients in shock, is a violaceous discoloration of the skin that is due to skin hypoperfusion. It most often manifests in the area around the knees but can also be seen in the ears and fingers. The patient received a diagnosis of acute myocarditis due to adenovirus, complicated by cardiogenic shock. She was treated with supportive care including mechanical ventilation, plasma volume expansion, and inotropic agents. The skin mottling disappeared within 24 hours after treatment (Panel B), and the left ventricular ejection fraction increased to 60% by day 3 of treatment. The patient had a full recovery.