How many times per minute does a blue whale's heart beat at its slowest, recorded during deep feeding dives?

Answer

2 beats per minute

Stanford researchers who suction-cupped a heart monitor to a wild blue whale found its heart nearly stops between beats on deep dives, then rockets to about 37 beats per minute at the surface — close to the physical limit for a heart that size.

Source: Goldbogen et al., PNAS (2019) / Stanford University