Due to the high prevalence of cardiovascular diseases and the corresponding prescription of cardiac drugs, side effects and interactions may occur in a substantial number of patients. They can be explained by either pharmacokinetic or pharmaco-dynamic drug interactions which may be desired, but may also be life-threatening. Despite the fact that the novel oral anticoagulants are well tolerated, several factors restricting the use of these drugs, such as renal failure, have to be considered. The use of antihypertensive drugs may be limited by concomitant use of drugs that either induce of inhibit enzymatic metabolism, respectively inhibit renal drug, electrolyte, and/or water excretion. In this respect, the interaction between beta-blockers, ACE inhibitors, angiotensin receptor blockers and thiazide diuretics with non-steroidal antiinflammatory drugs is especially important. Muscle disorders are frequent side effects in patients undergoing statin therapy and affect up to 5% of patients. They may manifest as mild myalgia, but also as life-threatening rhabdomyolysis.