The high costs of airborne flapping flight are reflected in a difference between the oxygen pulse (OP; amount of oxygen consumed per heart beat) during flight and that during terrestrial locomotion, as well as a difference in the relationship between heart rate (f(H)) and rate of oxygen consumption ((V) over dot O-2). We tested and failed to accept the hypothesis that there would be similar differences in the f(H)-(V) over dot O-2 and (V) over dot O-2-OP relationships during swimming under water and during walking for macaroni penguins ( Eudyptes chrysolophus (Brandt, 1837)). We suggest that this may be a result of the penguins having to overcome physical forces different from those experienced by volant birds and possibly a response to limited access to oxygen while porpoising or diving. This result has important implications for those who wish to use f(H) to estimate (V) over dot (O2) and hence metabolic rate in the field for this and similar species. To test the utility of the relationship, we compared our results with data obtained previously for this species, and we simultaneously measured (V) over dot (O2) in a respirometer and estimated (V) over dot (O2) from f(H) for 48 h. There was no significant difference in the f(H) -(V) over dot (O2) or (V) over dot O-2-OP relationships between the two studies or between (V) over dot O-2 estimated from f(H) and that measured using respirometry.