This is one of the reasons snow shoveling can be dangerous.
Blood pressure is the product of cardiac output (the amount of blood your heart pumps per minute) times the peripheral resistance (the resistance to blood flow - usually controlled by the constriction or relaxation of the small blood vessels - e.g. arterioles).
Blood pressure = Cardiac Output x Vascular Resistance
Usually, when you exert yourself there is an increase in heart rate and contractility of the heart - leading to increased cardiac output which will increase your blood pressure in accordance with the above relationship.
At the same time, as you exercise, you produce heat and also specific metabolites. This leads to dilation of the resistance blood vessels, and thus decreases vascular resistance. This blunts the rise in blood pressure.
In the winter your peripheral resistance vessels (e.g. in skin, your extremities, any body surface exposed to the cold) will contract, decreasing blood flow to those tissues. This helps to preserve body heat by decreasing the amount of warm blood being exposed to tissues that are exposed to the cold.
The problem is that if you start shoveling in the cold outside in the winter you will have an increase in cardiac output while at the same time having an increase in vascular resistance. This leads to a significant increase in blood pressure, and thus stress on larger blood vessels and on the heart. Eventually, as you shovel, you will generate metabolites and body heat that will blunt this vasoconstriction - but until you do you are at increased risk.
I post this because the principles are similar to those operative in the shower scenario.
That’s probably what claimed my grandmother. She had had a couple of heart attacks in her 80s, but the big one hit when she was shoveling snow, about 6 weeks before her 100th birthday.