For Blood there are a lot of variables that need to be considered before deciding how to tank them.
Blood Single Target Rotation
Make sure you have at least 50 runic power when using DS. Don't Death Coil if it will take you below 50 RP if DS is next on your priority list. You will usually have a HS to take you up to 50 before using DS to maximize it's damage. Of course if you have nothing else to use you're going to DS to get the runes on CD.
Group of 3 with focused DPS
Switch between the mobs and Heart Strike to your hearts content. My Pestilence may be in the wrong place, just keep an eye on your diseases and refresh as needed. For the bigger AoE pulls you would simply switch out the HS's for Blood Boils