This pilot randomized clinical study aims to evaluate the cardioprotective effects of a grape polyphenol concentrate in patients receiving anthracycline- and/or trastuzumab-based chemotherapy. Adult patients at high or very high risk of chemotherapy-induced cardiotoxicity will be randomized to receive either a grape polyphenol concentrate or placebo for three months, starting with chemotherapy. Cardiac function and cardiotoxicity will be assessed using echocardiographic parameters and circulating biomarkers at baseline, 3 months, and 6 months.

Inclusion Criteria:

• Female patients aged 30 to 75 years.
• Histologically confirmed breast cancer.
• Planned treatment with anthracycline- and/or trastuzumab-based chemotherapy.
• High or very high risk of chemotherapy-induced cardiotoxicity (≥20%), based on clinical assessment.
• Eastern Cooperative Oncology Group (ECOG) performance status 0-3.
• Ability to take oral study products.
• Willingness to comply with study procedures and follow-up visits.
• Written informed consent provided prior to any study procedures.

Exclusion Criteria:

• ECOG performance status of 4.
• Pre-existing severe cardiovascular disease that would interfere with study participation.
• Permanent atrial fibrillation or other clinically significant arrhythmias.
• Severe hepatic or renal impairment.
• Active central nervous system tumors or metastases.
• Uncontrolled arterial hypertension.
• Acute gastrointestinal diseases that may impair absorption.
• Known allergy or intolerance to grape products or study components.
• Participation in another interventional clinical trial that may interfere with the outcomes of this study.