Where is the Eustachian valve found?

In humans,the heart rate of $72$ beats/minute is regulated by which of the following?

Why do we call our heart myogenic?

Bicuspid and tricuspid valves are attached with inelastic fibres to the papillary muscles in the lumen of the ventricles. These fibres are . . . . . . .

All the components of the nodal tissue are autoexcitable. Why does the $SA$ node act as the normal pacemaker?

When the heart of a frog is removed from the body,it continues to beat for some time. Select the correct statement$(s)$ from the following:
$(i)$ The frog is a cold-blooded animal.
$(ii)$ The frog does not have a heart-based circulatory system.
$(iii)$ The heart has myogenic properties.
$(iv)$ The heart is self-excitable.