This study focuses on male and female patients being treated for breast cancer that is positive for the HER2 receptor which requires special treatments targeting that receptor. The problem is that these treatments, while effective for the cancer, can sometimes harm the heart. Because of this, patients have to undergo heart tests every three months during treatment, even if they have no history of heart disease or feel fine.

The guidelines for these regular heart tests were established decades ago when these treatments were first introduced, but research shows that most of these tests don't actually change the treatment plan. This suggests that many patients are going through unnecessary tests, which can cause stress, delay treatments, and increase healthcare costs.

To address this, the researchers propose a new study with 300 patients with HER2 positive breast cancer to test a more personalized approach to cardiac surveillance. Participants will be classified based on their risk of heart problems: low or intermediate. Instead of testing every patient every three months, those in the intermediate group will be tested every 4 months, and those in the low-risk group will be tested every 6 months. The researchers will compare this new approach to the current system to see if fewer tests are just as safe and effective.

The researchers will measure heart health, how well cancer treatments are completed, and how patients feel about having fewer tests. If this new approach works, it could save money and reduce the burden on female patients without risking their health.

Inclusion Criteria:

1. Stage 1-3 breast cancer (BC).
2. Age 18-79 years.
3. HER-2 positive BC with planned HER2 targeted therapy (HER2TT) for curative intent.

Exclusion Criteria:

1. Distant metastases detected clinically, radiographically, or histologically

2. Baseline echocardiogram images of insufficient quality for a quantitative assessment of left ventricular ejection fraction (LVEF)

3. Pre-existing cardiovascular disease, defined as:

   1. Prior myocardial infarction (even if LVEF has normalized)
   2. Prior heart failure (HF, including patients with preserved ejection fraction and normalized LVEF)
   3. Baseline LVEF <55%
   4. Atrial fibrillation
   5. Greater than moderate valvular disease (i.e., severe, or moderate-severe)

4. Cumulative anthracycline exposure ≥250mg/m2 before starting HER2TT

5. New York Heart Association Functional Class II, III or IV, or Eastern Cooperative Oncology Group score >2*

6. Symptoms potentially due to serious cardiac disease as per investigator's judgement* *Exclusion criterion adopted as they make clinical assessment less reliable to detect emergent HF.