Despite advantages of single-lead VDD systems, the frequency of implantation of these pacemakers in patients with symptomatic atrioventricular block and normal sinus rhythm continues to decline. Therefore, data comparing the atrial sensing performance of floating and fixed electrodes at identical activities are rare. The aim of the study was to investigate atrial sensing via floating and fixed atrial electrodes at identical activity levels (supine position, left side position, seated position, hyperventilation, standing, walking, fast walking, walking up and down stairs, for 1.5 min each) by beat-to-beat analysis in 24 h Holter ECG. A total of 42 patients were included in the study (22 patients with a DDD system; 20 patients with a VDD system). In 45% of the DDD systems and only in 20% of the VDD systems an intermittent atrial undersensing during activity was recorded (p = 0.0024). The intermittent atrial undersensing in both groups was detected significantly more often in the first 15 s of an activity (p < 0.001). Floating sensing reduced the frequency of atrial undersensing in the initial phase of the activity significantly compared to atrial sensing by a fixed electrode (p = 0.0347). This advantage of floating electrodes and the significant earlier atrial signal recognition by floating electrodes might be useful in future DDD pacemakers by combining a VDD electrode with a fixed atrial electrode.