Objectives: The objectives of this study were to examine whether there is a difference in the clinical findings of the lesion obtained by coronary angiography and OCT, to examine the association of OCT findings in the decision-making on additional optimization of PCI, to examine the association of OCT findings in the additional assessment of the significance of the lesion in multivessel coronary disease predicted for cardiac surgical treatment, and to examine whether there is an association between diastolic dysfunction and a higher frequency of inadequate PCI that requires additional optimization based on OCT. Study design: Cross-sectional survey with historical data Participants and methods: The study included patients who underwent OCT at the Department of Cardiovascular Diseases of the Osijek Clinical Hospital Center from 2021 to 2023. Results: The research was conducted on 62 patients, median age 67 years. The most common location of the lesion is the LAD in 52 (84%) cases. 39 respondents (63%) requested additional optimization. Three (5%) patients have a recommendation for cardiosurgical consultation based on OCT. There was a significant increase in the length of LAD (Wilcoxon test, P < 0.001), Lcx (Wilcoxon test, P < 0.001) and RCA (Wilcoxon test, P = 0.006) measured by OCT compared to coronary angiography. Regarding the proximal width, the values of the proximal width of the LAD (Wilcoxon test, P < 0.001) and the proximal width of the RCA (Wilcoxon test, P = 0.03) were significantly higher. Conclusion: The conducted research showed the important role of OCT in clinical practice, in the detailed assessment of lesions on the coronary arteries, in the management of PCI, and in the assessment of additional optimization in patients with coronary disease.