Delay in treatment seeking is recognized as a major contributor for Acute Coronary Syndrome (ACS) mortality in Indonesia. Despite the significance of timely treatment, decline in admission and delay in presentation of patients with ACS were consistently reported during the COVID-19 pandemic. These suggested that treatment seeking performance of patients during the pandemic might be different from the previous period. This qualitative study aimed to explore treatment seeking behaviour, barriers in seeking medical treatment, and experiences of patients with ACS in Yogyakarta, Indonesia during COVID-19 pandemic. In depth-interviews were carried out with 30 patients, who were hospitalized with ACS at one of the three selected hospitals in Yogyakarta during the pandemic period. Thematic analysis was performed to create vital explanations for treatment seeking practices of patients with ACS during pandemic. Three significant themes were identified: treatment seeking decisions, barriers in seeking medical treatment during COVID-19, and experiencing both good and bad impression from entering and staying in the hospital. The intensity of ACS symptoms and fear of COVID-19 infection dominated the delay in seeking medical treatment. Strict safety measures, religious belief, and fear of ACS helped patients overcome barriers and seek medical treatment during pandemic. ACS patients also had convenient medical care during the pandemic and believed medical staff would provide excellent care to them. However, visit restriction policy could cause psychological discomfort. Increase awareness of ACS symptoms and the risk of delays ACS treatment are essential to support patients' decisions to seek medical helps in a timely manner at any situations including pandemic. Interventions aim at alleviating psychological distress should also be designed and implemented to improve treatment experiences of ACS patients, who sought medical treatment during the pandemic crisis.