Leaving the median sternotomy wound open following cardiac surgery is employed to avoid cardiovascular compression. Horizontal struts can be used. Radiologists interpreting portable radiographs might be unaware of the open median sternotomy (OMS). To describe the frequency of radiographic signs of OMS and to increase awareness among radiologists to prevent misdiagnosis of pneumothorax and pneumomediastinum. Radiographs of 41 infants (17 girls/24 boys) with OMS were studied (age range 2 days to 8 months, mean 33 days). Central lucency and sternal edges were noted. Interclavicular distances before and after sternotomy were compared. Central lucency was seen in 25/41 (61%) children. Sternal struts were apparent in 27 (66%). In 14 without struts, central lucency was present in 8 (57%). In 27 children with struts, central lucency was present in 17 (63%) and absent in 10 (37%). Split sternal centers were identified in 6/41 (15%). The mean interclavicular distance was 23.5 mm (SD = 4.39) before sternotomy and 38.2 mm (SD = 7.0 mm) after sternotomy (P < 0.001). OMS has characteristic signs in the majority of cases. Recognition of these findings is useful and can prevent misinterpretation.