Which is the pacemaker of the frog's heart?

Mixing up of arterial and venous blood does not take place in a heart having

The 'Heart of Heart' is:

The blood pumped by the $A$ ventricle enters the $B$ artery,whereas the $C$ ventricle pumps blood into the $D$. Choose the correct option for $A, B, C$ and $D$.

What is the normal heart rate in a two-month-old infant?

Left auricle receives pure blood from the: