Similar to what you studied in skeletal muscle cells, the resting chemical disequilibriumof myocardial cellsis maintained by sodium-potassium pumps in the cell membrane. however, myocardial cells must also have these transporters in the cell membrane to return to the pre-activatedstate.

Ithink due to shortage of water

The answer to this will be from your lab notes/procedure. it would be best to ask another student who participated in the lab as we do not know what was done, what enzyme or if the temperature is celsius or fahrenheit. if i were to guess though i'd say the rate stopped due to enzyme denturing at high temperature

He used pea plants to study the patterns of heredity.