Potassium channels are membrane receptor sites for various drugs in the field of cardiovascular diseases. These channel proteins are extremely diverse, not only as regards their molecular structure but also as regards their function. Heterogeneous expression of various K+ channel subtypes is an integral part of cell specialization in different tissues. K+ channels interfere with most of the physiological processes of the cardiac muscle, of the vascular smooth muscle and of the endothelial cells. K+ channel blockers are antidiabetic agents but also antiarrhythmic drugs. K+ channel openers are used in the treatment of hypertension and most recently in the treatment of coronary heart disease. In the experimental setting, K+ channel openers afford cytoprotection during ischaemia. This exciting property opens a new field in clinical research.