IgG4-related disease (IgG4-RD) is a recently recognized fibro-inflammatory condition characterized by tumefactive lesions, storiform fibrosis, elevated serum IgG4 concentrations, and dense, lymphoplasmacytic, infiltrate-rich, IgG4-positive plasma cells [1]. IgG4-RD was first reported in Japan in 2003 in a pathophysiological study of patients with autoimmune pancreatitis [2]. IgG4-RD has been reported in various organ systems, including the biliary tree, salivary glands, periorbital tissues, kidneys, lungs, lymph nodes, meninges, breast, prostate, thyroid, heart, vessels, and skin [1,3]. IgG4-RD has also been reported in large and small arteries as periarteritis, which can cause inflammation in the adventitia [4]. IgG4-related coronary periarteritis causes coronary artery narrowing and aneurysm and pericoronary pseudotumor formation [4], [5], [6]. In this case report, we describe a patient with rapid IgG4-related coronary artery aneurysm progression and describe the multimodal presentation and pathology of the disease.