27. The plateau phase of the normal contractile cell action potential is mostly due to:

38. Name this structure:

32. Name the chamber:

46.  Name the structures:

28. When a cardiac muscle action potential is present, but there is insufficient calcium to result in mechanical action (muscle contraction), the result is described as:

25. A dilatation at the bases of aorta & pulmonary trunk that presumably provides space for the semilunar valve apparatus when opened is called the:

30. A fixed, split S-2 can be due to:

26. Final ventricular filling during the very end of diastole coincides with: .

47. Name the valve:

31. Name the chamber: