Safety, Tolerability, and Exploratory Efficacy of AGP100 in Patients With Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)

This trial is conducted in patients with an inherited heart rhythm disorder called catecholaminergic polymorphic ventricular tachycardia (CPVT). This condition causes the heart to beat dangerously fast during situations of physical or emotional stress. CPVT is a serious condition that can limit the length and quality of patients' lives. Current treatment does not always prevent the abnormal heart rhythms that can occur as part of CPVT during strenuous exercise or stress, so new and improved medications are needed. The main questions that the trial will answer are: * How safe and tolerable is the drug AGP100; i.e, what medical problems do patients experience when taking the drug? * Does the drug help CPVT patients to maintain a normal heart rhythm while they are exercising? * How does the drug affect the levels of key heart cell signalling molecules? Patients with a diagnosis of CPVT who are aged between 18 and 75 and experience abnormal heart rhythms during exercise, despite taking a stable dose of the medication(s) prescribed by their doctor for their CPVT can take part in this trial. Participants should have normal kidney and liver function and not have high blood pressure or a diagnosis of structural heart disease. Women who are pregnant or breastfeeding cannot take part in the study. Participants who may become pregnant (and their partners) need to use highly effective methods of contraception during the study and for 90 days after the study ends. Participants will take part in the study for ten weeks. During this time, participants will be asked to take three different doses of the the drug (AGP100), as well as their normal heart medication. The drug is an oral capsule and each different dose will be taken once a day for 13 days. The study starts with participants taking a low dose for 2 weeks, then a medium dose and then a high dose. At each dose, participants will undergo a clinical examination, report any potential side effects and the treating doctor wi