Smooth muscle is present in one form or another in most organs, and its contractile activity is vital for normal functioning of the body. To be able to perform the multitude of tasks required of the organs, smooth muscle cells vary widely in their patterns of activity. In blood vessels, a continuous and maintained activity is required, whereas in the uterus only occasional bursts of activity are needed. Some tissues act as a unit (urinary bladder), whereas others have localized contraction (arterioles) or a peristaltic wave of contraction passing through them (intestine) [1, 2]. Functionally, smooth muscle can be broadly classified into tonic and phasic types [2–4]. Tonic smooth muscle cells do not normally generate action potentials. They have a relatively high content of the LC-17b isoform of the alkali myosin light chain, and have myosin heavy chains that lack a 7-amino-acid insert. These slow myosin isoforms have a higher affinity for Mg++ ADP and this may contribute to the “latch” state and slow shortening velocity [4, 5].