Fig. 2. Mean heart rate (f_H) ± S.E.M. during (A) post-dive surface intervals and (B) dives in control and pharmacologically blocked harbour seals (N=5). Heart rate data from control groups were combined to give the mean f_H indicated by the horizontal lines, although statistical analyses were performed on controls for each data set. ^* indicates values significantly different from the control group within dive states (P<0.05). For each treatment, the dive f_H was significantly lower than the surface interval f_H. , seals treated with -adrenergic blocker; ß, seals treated with ß-adrenergic blocker; mu+, seals treated with muscarinic and -adrenergic blockers combined; mu+ß, seals treated with muscarinic and ß-adrenergic blockers combined.