Severe adverse effects associated with the use of calcium channel blockers do not occur very often. Sometimes nifedipin produces hypotension, tachycardia, and headache, whereas verapamil, gallopamil, and dilitiazem show more negative chronotropic effects such as bradycardia or sinuatrial and atrioventricular nodal conduction disturbances. Gastrointestinal side effects are constipation after verapamil and stomach problems after gallopamil.