Hearts are of several types. In some invertebrates the heart is simulated by the nervous system to do its work. Such hearts are called Neurogenic hearts. The Human heart is myogenic. i.e, it recieves the stimuli for contraction from the muscular node called sinu-auricular node or pace maker.

Aestivation is summer sleep. Many organisms like the snails do not find it comfortable in summer. They withdraw and lead a life with reduced BMR (basic Metabolic Rate) in a state of  dormancy.