The cells of the heart that contain contractile filaments are called _____ cells. (Fill in the blank)

The answer to question 1  myocardial

The answer to question 2  C
In second-degree AV block type I, the PR interval is inconstant and the PR interval after a nonconducted P wave is shorter than the interval preceding the nonconducted beat.
Although progressive lengthening is a phrase that was used for many years to describe the behavior of the PR intervals associated with second-degree AV block type I, use of this terminology is no longer recommended; rather, the term inconstant or generally progressive PR intervals is recommended. Use of the term inconstant or generally progressive PR intervals is important because many type I AV blocks are atypical, missing one or more of the features of the classic Wenckebach phenomenon. For example, the second conducted PR interval after a blocked impulse may fail to show the greatest increase in length; instead, the PR interval may actually shorten and then lengthen in the middle of a grouped beating pattern. Alternately, the duration of the PR intervals may show no obvious change in the middle or for a few beats just before the end of a group.

The answer to question 3  segment

The answer to question 4  A
In second-degree and third-degree AV blocks, there are more P waves than QRS complexes and the P waves occur regularly.

All are correct

Happy to help