Introduction With growing sophistication of eHealth platforms, medical information is increasingly shared across patients, health care providers, institutions and across borders. This implies more stringent demands on the quality of data entry at the point-of-care. Non-native English-speaking general practitioners (GPs) experience difficulties in interacting with international classification systems and nomenclatures to facilitate the secondary use of their data and to ensure semantic interoperability. Aim To identify words and phrases pertaining to the heart failure domain and to explore the difficulties in mapping to corresponding concepts in ICPC-2, ICD-10, SNOMED-CT and UMLS. Methods The medical concepts in a Belgian guideline for GPs in its French version were extracted manually and coded first in ICPC-2, then ICD-10 by a physician, an expert in classification systems. In addition, mappings were sought with SNOMED-CT and UMLS concepts, using the UMLS SNOMED-CT browser. Results We identified 143 words and phrases, of which 128 referred to a single concept (1-to-1 mapping), while 15 referred to two or more concepts (1-to- n mapping to ICPC rubrics or to the other nomenclatures). In the guideline, words or phrases were often too general for specific mapping to a code or term. Marked discrepancy between semantic tags and types was found. Conclusion This article shows the variability of the various international classifications and nomenclatures, the need for structured guidelines with more attention to precise wording and the need for classification expertise embedded in sophisticated terminological resources. End users need support to perform their clinical work in their own language, while still assuring standardised and semantic interoperable medical registration. Collaboration between computational linguists, knowledge engineers, health informaticians and domain experts is needed.