Despite the availability of diagnostic modalities such as transesophageal echocardiography, computed tomography or magnetic resonance imaging up to 30% of patients with acute aortic dissection remain undiagnosed before death. A novel immunoassay of serum smooth muscle myosin heavy chain was recently developed as a potential diagnostic tool for the detection of aortic dissection. The immunoassay was applied in two patients with an acute chest pain syndrome but no initial clinical suspicion of aortic disease. In both patients myocardial ischemia was ruled out by laboratory, electrocardiographic and echocardiographic examinations. In the first patient both dilation of the aorta and long-standing arterial hypertension were known; however, it was not before 48 h until dissection was suspected and a spiral-CT was performed demonstrating a localized ascending aortic dissection. At this time (48 h after onset of symptoms) the smooth muscle myosin heavy chain concentration in the serum was close to normal. In the other patient there was neither a suggestive history nor any clinical sign of aortic dissection. Widening of the abdominal aortic wall on an ultrasound examination was the key to the incidental diagnosis of a clinically unsuspected type B dissection. The serum test 12 h after onset of pain revealed elevated (diagnostic) serum levels of smooth muscle myosin heavy chains. Both cases exemplify important gaps in the diagnostic strategy for the detection of acute aortic dissection. A novel immunoassay for smooth muscle myosin heavy chains provides rapid and reliable diagnostic information especially in patients without clinically suspected aortic dissection and may avoid limitations in the diagnostic work-up of patients with acute aortic disease, if used early in the evaluation of patients with chest pain syndromes.