29. This figure shows the principal coronary blood vessels. Which one is the left coronary artery (LCA)? B. 8 C. 5 D. 3 E. 1 will cause a more severe myocardial infarction (MI) 30. Obstruction of the than the obstruction of any of the others A. left marginal vein B. left coronary artery (LCA) C. posterior interventricular vein D. anterior interventricular branch E. circumflex branch Solution 29. D. 3 30. B. left coronary artery 31. A. cardiac muscle fibers have striations 32. C. Sinatrial (SA) node. 33. B. . The tendinous cords. 34. e. They have about the same endurance as skeletal muscle fibers. 35. SA node, AV node, AV bundle, Purkinje fibers, cardiocyte in LV 36. A. Na+ inflow 37. E. slow CA2+ channels.