Could my exercise headache be a sign of heart disease?

In some cases, yes. Cardiac cephalgia — headache as the only expression of myocardial ischemia — is induced by exertion in about two-thirds of cases and typically lasts under 30 minutes.¹ It tends to appear in patients over 50 with cardiovascular risk factors. If you have those risk factors and develop exertion-triggered headache without a clear neurological reason, your clinician may also order cardiac evaluation.