@misc{indiciae71e12350494b,
  title = {Concealed extrasystoles.},
  author = {H D Friedberg},
  year = {1969},
  doi = {10.1016/0002-9149(69)90418-4},
  url = {https://pubmed.ncbi.nlm.nih.gov/4183957/},
  note = {Source identifier: 4183957}
}