In this ECG of a dog, the P waves and QRS complexes (R) are dissociated from one another (there is no apparent relationship between them). The atrial rate varies from ~100 to 150 bpm (P-P interval varies from 0.6 to 0.4 second), and the ventricular rate is steady and in the low 40s (R-R interval = 1.46 seconds), with normal QRS-T complexes (nodal escape rhythm).