-Rate-responsive pacemaker with an unexpected chronotropic response-.

: The pacemaker with rate-responsiveness was a great advance in cardiac stimulation, however, the choice of the best biosensor is still object of research. A 35 year-old woman with a responsive pacemaker implanted due to a complete heart block after interventricular septal defect surgical correction was admitted. The pacemaker showed improper cronothropic response with high frequency due to biosensing malfunction. Malfunction related to muscle stimulation in the generator pocket and a high response rate. A palliative procedure was made until the end of pregnancy, by reducing the sensitivity of biosensing.