Question about vasodilators

I have a few questions I am stuck on and can't seem to understand clearly. How can calcium channel blockers side effects produce both tachycarda and bradycardia depending on the medication?

For example: Cardizem produces bradycardia

Nimotop produces tachycardia

If they both dilate coronary arteries how can they produce two different effects? I am really confused how to determine when you would expect to see tachycardia or bradycardia.

This is what I understand: Vasodilation relaxes and opens up the vessels which eases the passage of blood through the vessel. The BP drops which decreases the workload of the myocardium. Vasodilators can act on the veins, arteries, or both which affects preload or afterload. Is this what determines if we see bradycardia or tachycardia?

My thinking is that if you are dilating your BP is going to drop which decreases the workload of the heart causing bradycardia, but I know there is a reason for the tachycardia somewhere. I have a feeling I am way off center so if anybody could explain it simply it would be greatly appreciated. Thanks