Reliable sensing of the P wave is an essential requirement for the appropriate functioning of any device that uses atrial tracking to provide AV synchrony. However, a single measurement of the P wave amplitude, either at implantation or during follow-up, may not be a reliable reflection of the P wave amplitudes that occur during daily life. The P wave amplitude histogram is a new feature that automatically measures the P wave amplitude at regular intervals and provides the distribution of these measurements. This enables the assessment of the smallest P wave amplitudes that occur. Two populations were studied: 104 patients with a fixed atrial lead and a DDDR pacemaker and 100 patients with a single pass VDD lead and a VDD pacemaker. Both pacemakers incorporate the P wave amplitude histogram feature. Data in the P wave amplitude histogram were compared with a single measurement of the P wave amplitude at each follow-up. Programming of a 100% safety margin based on a single measurement of the P wave amplitude provided reliable atrial sensing in only 72% and 43% of the patients of both populations, respectively. Data continued in the P wave amplitude histogram may be a useful adjunct for the optimal programming of atrial sensitivity.