Anthracyclines such as doxorubicin are chemotherapeutic molecules are also widely incorporated in many chemotherapy protocols. However, their clinical use is still limited by time- and dose-dependent cardiotoxicity. Herein the inventors have determined the therapeutic potential of acidic nanoparticles (NPs) in doxo-treated cardiac cells. In particular, they have identified a set of grafted nanoparticles as non-toxic and which rapidly internalize into lysosomes in cardiac cells. Such NPs improve lysosomal acidification and autophagic flux blockade caused by bafilomycin A1, chloroquine and doxorubicin, resulting in reduced oxidative stress, preserved mitochondrial integrity and improved cell survival. Thus, the invention relates to a biocompatible and biodegradable nanoparticle having a diameter of 100 nm or less, wherein the nanoparticle is selected from: a poly(lactic-co-glycolic acid) (PLGA) nanoparticle, a poly(lactic acid) (PLA) nanoparticle, a poly(glutamic acid) (PGA) nanoparticle, a polycaprolactone (PCL) nanoparticle, and/or a polyester nanoparticle; for use in a method for treating or preventing a cardiomyopathy or anthracycline cytotoxicity.