Question

when do the atria contract​

Answer 1

Answer:

Most contracts only need to contain two elements to be legally valid: All parties must be in agreement (after an offer has been made by one party and accepted by the other). Something of value must be exchanged -- such as cash, services, or goods (or a promise to exchange such an item) -- for something else of value.

Answer 2

Explanation:

At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract (atrial systole), and each atrium pumps blood into the ventricle 'below' it.