I got a heart ct scan done and the calcium score is 0. however, in that report there is the following line: mediastinum: calcified nonenlarged subcarinal lymph node. is this worrisome ? (i've no issues related to this?

Probably not important, since non-enlarged calcified lymph nodes can be due to a variety of conditions, including past lung infection, past tuberculosis, and other entities such as sarcoidosis. However, the cardiac CT does not include the entire chest. If you and your doctor are worried, then get a CT CHest now, or a follow up CT in 4-6 months.