Box B of the Diver Medical questionnaire runs to four lines, and one asks whether you are over 45 and have high blood pressure. Tick it and all three pages go to a doctor for a written evaluation, which is where the decision belongs. DAN Southern Africa puts the clinical threshold at average readings above 140 systolic and 90 diastolic.
The answer underneath the question is less dramatic than the forum threads suggest. The Diving Medical Guidance behind the form is direct about it. Treated hypertension with adequate control is acceptable in diving, absent other risk factors that would trigger coronary screening. DAN Southern Africa frames the same position as three conditions: blood pressure controlled, exercise capacity unaffected, and no damage to the heart, brain, kidneys or blood vessels. Hypertension on its own is a referral rather than a refusal.
What does the dive medical form ask about blood pressure?
The Diver Medical Participant Questionnaire has ten questions on page one. The Diver Medical Screen Committee revised it in July 2020, with the Undersea and Hyperbaric Medical Society and DAN behind it. Blood pressure reaches that form by three separate routes.
Question one covers problems with the lungs, breathing, heart or blood, and a yes opens Box A. That box asks about angina, chest pain on exertion, heart failure, immersion pulmonary oedema, heart attack, stroke, and medication taken for any heart condition. Question two is age alone. Over 45 opens Box B, which pairs high blood pressure with smoking, high cholesterol and a family history of cardiac death before 50.
Question ten is the one people miss. It asks about prescription medication, with exceptions only for birth control and most anti-malarials. A yes there requires a physician's evaluation at any age. A 32-year-old on a single blood pressure tablet reaches the doctor through question ten, not through Box B. Age does not get you out of it.
A yes anywhere on the form means carrying all three pages to a physician, who ticks Approved or Not approved and signs. Page three sends that doctor to uhms.org for condition-specific guidance. Asthma travels the same route through Box A, and we have written up how that condition is assessed separately. Our FAQ page carries the short version of the dive medical question.
What does DAN say about hypertension and diving?
DAN Southern Africa's position is specific. Diving works when the pressure is controlled, when exercise capacity is unaffected, and when the heart, brain, kidneys and blood vessels show no damage. The reasoning is about sudden incapacitation rather than the reading itself. A number on a cuff does not disable a diver at 18 metres. An ischaemic event does.
The Diving Medical Guidance lists hypertension among the conditions to investigate, so as to exclude a disqualifying condition. It sits alongside exertional chest pain, unexplained syncope, a heart murmur and early cardiac death in the family. The guidance adds that asymptomatic candidates over 45 with coronary risk factors should see a physician. A predicted five to ten year cardiovascular event risk above 10 percent should prompt investigation for coronary disease.
Exercise capacity gets a hard number. The guidance describes sustaining 6 MET, roughly an oxygen consumption of 21 mL/kg/min, as a pragmatic expectation for a recreational diver. The form tests the same thing in plainer language at question three: walking 1.6 kilometres in 14 minutes, or swimming 200 metres without resting.
Does blood pressure medication change the answer?
DAN's guidance works by drug class. The drug itself is rarely the problem. Its side effects, and the condition it treats, are what a dive doctor weighs.
- Diuretics. DAN's concern is water loss. In hot conditions these drugs can cause excessive dehydration, and dehydration is associated with decompression sickness risk. A Highveld summer afternoon at a dive site qualifies. Any change to dosage on diving days is a conversation with the prescribing doctor.
- Beta blockers. These carry the heaviest caution. DAN states they can reduce the heart's capacity for exercise and therefore affect exercise tolerance. That is the exact quality the evaluation sets out to establish, so stress testing before clearance is common.
- ACE inhibitors. Fewer adverse effects overall, with one specific problem: DAN notes they can produce a cough and airway swelling, both awkward with a regulator in your mouth.
- Calcium channel blockers. DAN reports that these do not typically pose problems for divers, with dizziness on standing as the main caveat.
- Anticoagulants. Not a blood pressure drug, but they arrive in the same conversation. DAN warns that excessive bleeding can follow even a seemingly benign ear or sinus barotrauma.
None of that is a reason to start, stop or adjust anything you take. It is a reason to book the appointment with someone who has read the guidance.
What does immersion itself do to the heart?
Getting into the water changes your circulation before you descend a metre. The Diving Medical Guidance puts it directly. Immersion itself increases cardiac preload, as does peripheral vasoconstriction with a rise in blood pressure. Those changes are typically accompanied by sustained mild to moderate exercise.
Cold water drives the vasoconstriction harder, so an inland freshwater dive in winter asks more of the cardiovascular system than a warm pool session. Stack preload, vasoconstriction and finning against a current on top of an untreated cardiac problem, and the loading is real. The same guidance records that almost 30 percent of recreational diving fatalities have a cardiac event as the disabling injury. That figure explains why the cardiovascular section of the form runs so long.
Why does immersion pulmonary oedema get a mention?
It appears by name in Box A, which surprises people who have dived for years without hearing of it. DAN Southern Africa describes hydrostatic pressure pushing substantially more blood into the central body, increasing heart size and cardiac filling pressure. Peripheral vasoconstriction, caused by cold water or by high blood pressure, raises pulmonary capillary pressure further. Blood plasma then leaks into the alveoli, where gas exchange happens.
The Diving Medical Guidance lists hypertension first among the risk factors. Valvular disease, diastolic dysfunction, cardiomyopathies, pulmonary hypertension, over-hydration, cold stress, constrictive garments and increased breathing resistance follow it. Symptoms include breathlessness, difficulty inhaling, coughing that may produce pink frothy sputum, and confusion. They can worsen during ascent. DAN Southern Africa's management is to surface with the diver, give 100 percent oxygen, keep them sitting up and warm, and activate emergency services. No fluids.
The follow-up rules are strict. A single episode may contra-indicate further diving if no modifiable risk factors are found. Repeated cases count as a strong contra-indication, and anyone with that history belongs in front of a physician trained in diving medicine.
Who makes the call?
Not the dive shop. We book courses, teach them and check that the paperwork is complete and signed. Fitness to dive is a medical judgement, made by a doctor with your history in front of them.
DAN says the same about itself. Its guidance states plainly that DAN is not a regulatory agency and does not set physical standards for scuba diving. Responsibility for the decision is left to the individual, the physician and the dive provider. Ask for a doctor trained in diving medicine where you can find one. Where you cannot, take all three pages, since page three carries the references.
If you already dive and your blood pressure has changed since your last form, the same route applies. Continuing education courses ask for the questionnaire again, and the honest answer is the one that protects you.
Sources
- DAN Southern Africa, High Blood Pressure: Can I Dive? The 140/90 threshold and the three conditions under which diving is considered reasonable.
- Diving Medical Guidance to the Physician (DAN, 2021) Cardiovascular screening goals, the treated-hypertension position, the 6 MET exercise expectation, the 30 percent cardiac fatality figure, and the immersion pulmonary oedema risk list.
- DAN, Cardiovascular Medications and Diving The drug-class detail on diuretics, beta blockers, ACE inhibitors, calcium channel blockers and anticoagulants.
- Diver Medical Participant Questionnaire (version 2026-01-01) The exact questions, Box A and Box B wording, and the Physician's Evaluation Form.
- UHMS, Recreational Diving Medical Screening System How the three-part system fits together and what the physician guidance is for.
- DAN Southern Africa, Immersion Pulmonary Oedema Mechanism, symptoms and in-water management.
Frequently Asked Questions
Does high blood pressure stop you doing a scuba course?
Not by itself. The Diving Medical Guidance treats hypertension as a condition to investigate. Treated hypertension with adequate control is acceptable in diving where other risk factors do not trigger coronary screening. The decision is the doctor's, on the Physician's Evaluation Form.
Do you need a doctor's letter if you take blood pressure tablets?
Question ten of the Diver Medical questionnaire covers prescription medication, excluding birth control and most anti-malarials. A yes there requires a physician's evaluation regardless of your age, so the signed form travels with you to the course.
What blood pressure reading is too high to dive?
No single reading decides it. DAN Southern Africa defines high blood pressure as an average above 140 systolic and 90 diastolic. The diving assessment turns on control, exercise capacity and end-organ damage rather than one reading.
Can you dive with a pacemaker?
The Diving Medical Guidance says candidates with pacemakers may be able to dive, while pacemaker-dependent candidates should consider the risks carefully. The device must be certified by its manufacturer to withstand the pressure changes. The guidance calls diving beyond 30 metres with any of them unwise.
Can you dive after a heart attack?
The guidance gives a route rather than a yes or no. A candidate who has been successfully revascularised may be suitable for diving if inducible ischaemia can be excluded and adequate exercise capacity demonstrated.
Does scuba diving raise your blood pressure?
Immersion increases cardiac preload, and peripheral vasoconstriction raises blood pressure, with cold water strengthening that effect. Those changes usually come alongside sustained mild to moderate exercise, which is part of why the cardiovascular questions exist.
This is general information, not a substitute for a dive medical or advice from a doctor trained in dive medicine. In an emergency, contact your local emergency services and DAN Southern Africa on +27 82 810 6010.
Reviewed September 2026. Devon Ford runs Scuba Evolution, a PADI 5 Star Dive Centre in Glenvista, Johannesburg.
