This study looks at how safe and effective a new medicine, AZD0780, is for adults with a condition called heterozygous familial hypercholesterolemia (HeFH). People with HeFH have high levels of LDL-C, also known as "bad cholesterol." AZD0780 is a small molecule that lowers LDL-C in the blood. During the study, some participants will receive AZD0780 while others will receive a placebo (a fake medicine). Neither the participants nor the researchers will know who gets which treatment until the study ends.

• The study lasts about 56 weeks, including a screening period of up to 14 days.
• Participants will be treated with AZD0780 or placebo for 52 weeks, with a follow-up period of 10 days.
• Participants must be at least 18 years old and have a confirmed diagnosis of HeFH with specific LDL-C levels.

Participants will need to take their assigned medication once daily and continue their current cholesterol-lowering treatments. Regular check-ups at one of the 170 study centers will be required. This study aims to recruit about 405 participants across 25 countries.