What is active relaxation of cardiac muscle?

if the basic contraction mechanism for cardiac muscle is the same as for skeletal, then it might refer to the fact the ca2+ is actively pumped back into the things (i forgot what they were called) in which they are contained and released upon depolarization.

 

Sarcoplasmic reticulum (SR).

 

Im guessing that refers to the diastole phase of heart contraction.
The "things" bewitched is referring to might be the myocardium? I believe that during diastole that Ca is actively pumped out of the myocardium, hence active.

This is a very vague guess though, so take it with a heaping of salt.