Your doctor is following best practices. Chemotherapy can cause venous thrombosis (blood clots) which can potentially cause strokes. Heparin can prevent clots from forming. Pre-medications like heparin and others are in people’s best interests.

Heparin has a very short 1.5 hour half-life and can be out of your system in 6-8 hours, so there’s little to no longterm bleeding risk.