An implantable leadless pacemaker system, comprising: a leadless pacemaker device having a housing; at least one attachment member on the housing for attaching the pacemaker device to an inner wall of a heart; a first electrode and a second electrode, configured to detect P-waves generated by a chamber of a heart in which the pacemaker device is implanted and far-field R-waves in an adjacent chamber of the heart; a first sensing channel in the housing, configured to sense P-waves detected by the first and second electrodes and configured to reject far-field R-waves detected by the first and second electrodes, and having a first band-pass filter with a first frequency range; a second sensing channel in the housing, configured to sense far-field R-waves and P-waves detected by the first and second electrodes and having a second band-pass filter with a second frequency range that is different from the frequency range of the first sensing channel; and a processor configured to distinguish between P-waves and far-field R-waves based on data from the sensing channels and to generate a timing signal for timing atrial pacing therapy delivered by the pacemaker; wherein the first band-pass filter of the first sensing channel has a frequency range with a low end of approximately 10 Hz to approximately 40 Hz and a high end of greater than approximately 30 Hz and a low sensitivity threshold of about 1 mV, and wherein the second band-pass filter of the second sensing channel has a frequency range with a low end of approximately 0.5 Hz to approximately 20 Hz and a high end of greater than approximately 20 Hz and a high sensitivity threshold of about 0.15 mV. a leadless pacemaker device having a housing; at least one attachment member on the housing for attaching the pacemaker device to an inner wall of a heart; a first electrode and a second electrode, configured to detect P-waves generated by a chamber of a heart in which the pacemaker device is implanted and far-field R-waves in an adjacent chamber of the heart; a first sensing channel in the housing, configured to sense P-waves detected by the first and second electrodes and configured to reject far-field R-waves detected by the first and second electrodes, and having a first band-pass filter with a first frequency range; a second sensing channel in the housing, configured to sense far-field R-waves and P-waves detected by the first and second electrodes and having a second band-pass filter with a second frequency range that is different from the frequency range of the first sensing channel; and a processor configured to distinguish between P-waves and far-field R-waves based on data from the sensing channels and to generate a timing signal for timing atrial pacing therapy delivered by the pacemaker; wherein the first band-pass filter of the first sensing channel has a frequency range with a low end of approximately 10 Hz to approximately 40 Hz and a high end of greater than approximately 30 Hz and a low sensitivity threshold of about 1 mV, and wherein the second band-pass filter of the second sensing channel has a frequency range with a low end of approximately 0.5 Hz to approximately 20 Hz and a high end of greater than approximately 20 Hz and a high sensitivity threshold of about 0.15 mV.