Medicinal plants extracts have been used in patients with heart failure, systolic hypertension, angina pectoris, atherosclerosis, and arrhythmias especially in developing or remote areas. Their use is also increasing in Western countries, as widely reported by the literature, often without informing their medical doctors. The increased popularity of natural products that are used as self-made treatments has revived interest in research into the risk and opportunities for this treatment modality for cardiovascular diseases. They are often very popular but health care professionals, notably specialists, understandably feel uncertain about their risks in the era of evidence-based and precision medicine.

Many substances found in herbs can have various effects on the heart or drugs used to treat the heart. Potentially serious adverse effects reported in the literature include arrhythmias, arteritis, cardiac glycosides overdose, chest pain, congestive heart failure, hypertension, hypotension, myocardial infarction, over-anticoagulation, pericarditis, and death. As is well known in pharmacognosy and clinical herbal medicine, there are many plant secondary metabolites with adverse cardiac pharmacological effects, such as the entire category of cardiotonic heterosides, diterpene alkaloids, phenethylamines or oligomeric procyanidins, and strong modulators of cytochromes as those found in St. John's wort extracts (Hypericum perforatum L.) or grapefruit juice (Citrus paradise Macf.).

The purpose of this Special Issue is to provide updated information on the risk and opportunities of using medicinal herbal extracts to treat arrhythmias and related cardiac disease, including adverse reactions, synergistic or antagonistic effects, reductions of side effects in order to explore their therapeutic potential, and evaluation future research opportunities. Original research and review articles are welcome.

Potential topics include but are not limited to the following:

• Acute medicine, toxicology, and arrhythmias
• Development of new antiarrhythmic drugs
• Herbal extracts for treatment of arrhythmias
• Traditional herbal medicine for the treatment of arrhythmias