Immunoglobulin G4-related disease (IgG4-RD) is a systemic disorder characterized by multiorgan fibrosis with IgG4-producing plasma cells, increased IgG4 serum concentration, and responsiveness to steroid therapy. Involvement of the pancreas, salivary glands, orbit, aorta, and other sites has been well documented in the literature; however, there have been limited reports of cases involving the coronary arteries. We report the case of a 53-year-old Hispanic man who was brought to the emergency center and diagnosed with sudden cardiac death. Autopsy was subsequently performed, revealing multiorgan involvement by IgG4-RD, including involvement of the coronary arteries. The inflammation and fibrosis, in combination with concomitant atherosclerotic disease, resulted in severe stenosis of the coronary arteries. Two of the coronary arteries were further occluded by thrombosis. These factors led to cardiac hypoperfusion, myocardial infarction and, ultimately, sudden cardiac death. Fatal involvement of the coronary arteries has not been previously reported, raising a new concern for a severe complication of IgG4-RD.